MUTATIONS HARVARD

3U<\

Bulletin of the

Museum

of

Comparative Zoology

AT HARVARD ^COLLEGE.

Vol. LII. No.

13.

REPORTS OX THE

SCIENTIFIC

RESULTS OF THE EXPEDITION TO THE EASTERN TROPICAL

PACIFIC, IN

CHARGE OF ALEXANDER

AGASSIZ,

BY THE

U. S.

FISH COMMISSION STEAMER "ALBATROSS," FROM OCTOBER,

1904,

TO MARCH,

1905, LIEUT.

COMMANDER

^L.M.

GARRETT,

U.S.N.,

COMMANDING.

XX.

MUTATIONS IN CERATIUM.

By Charles Atwood

Kofoid.

With

Four Plates.

[Publishedby^PermissionofGeorge M. Bowebs,U. S. Fish.Commissioner.]

CAMBRIDGE, MASS.,

^U.S.A.:

PRINTED FOR THE MUSEUM.

September, ^1909.

ern Tropical

_Pacific,in

charge of Alexander

_Agassiz,

by the

U. S.

Fish Commission Steamer "Albatross," from _October,

1904, to

March,

1905,

Lieutenant Commander

L.

M. Garrett,

U.S.N.,

Commanding, published or

in

preparation: —

A. AGASSIZ. V.^b GeneralReport ontheEx- pedition.

A.AGASSIZ. I.1 Three Letters to"Geo. M.

Bowers, U.^S.FishCom.

A.AGASSIZandH.L.CLARK. TheEchini.

H

^B.BIGELOW. XVI.¹⁶ The Medusae.

H.B.BIGELOW. TheSiphonophores.

R.P.BIGELOW. TheStomatopods.

O. CARLGREN. TheActinaria.

8. F.CLARKE. VIII.⁸ TheHydroids.

-W.R.COE. TheNemerteans.

L.J.COLE. XIX.^J9 ThePycnogonida.

W. H. DALL. XIV.¹⁴ TheMollusks.

C.R.EASTMAN. VII.⁷ TheSharks' Teeth.

B.W.EVERMANN. TheFishes.

W.G.FARLOW. ^TheAlgae.

S.GARMAN. XII.¹² TheReptiles.

H.J. HANSEN. The_Cirripeds.

H.J. HANSEN. TheSchizopods.

8.

HENSHAW.

TheInsects.

W.E.HOYLE. TheCephalopods.

C.A.KOFOID. III.³IX.⁹XX.²⁰TheProtozoa.

P.

KRUMBACH.

TheSagittae.

R.

VON

LENDENFELD. TheSiliceousSponges.

H.LUDWIG. TheHolothuriane.

H.LUDWIG. TheStarfishes.

H.LUDWIG. The_Ophiurans.

G.W.MULLER. TheOstracods.

JOHN MURRAY

and G. V. LEE. XVII."

The Bottom Specimens.

MARY

J. RATHBUN. X.¹⁰ The Crustacea Decapoda.

HARRIET

RICHARDSON. II.² The_Isopods.

W.E.RITTER. IV.⁴ TheTuuicates.

ALICE ROBERTSON. ^TheBryozoa.

B.L.ROBINSON. ^ThePlants.

G. O.SARS. The_Copepods.

F. E.SCHULZE. ^XI.11 The Xenophyophoras.

H. R.SIMROTH. ^ThePteropodsandHetero- pods.

E.C.STARKS. ^{XIII.13 Atelaxia.}

TH.STUDER. TheAlcyonaria.

JH.THIELE. XV.¹⁵ Bathysciadium.

T.W.VAUGHAN. ^{VI.« TheCorals.}

R. WOLTERECK. ^XVIII.18 The Amphipods.

W. McM.

WOODWORTH.

TheAnnelids.

iBull.M.C. Z.,Vol. XLVL,^No.4,April, 1905,22pp.

* Bull.M.C. Z.,Vol.XLVL,^No.6,July,1905,4_pp.,1pi.

» Bull.M._{C. Z.,}Vol.XLVL,^No.9,September,1905,5pp., 1pi.

* Bull.M.C.Z.,Vol.XLVL, ^No.13,January,1900,22pp.,3pis.

BMem.M.^C.Z.,Vol.XXXIII.,January, 1906,90pp.,96_pis.

s Bull.M.C. Z., Vol. L.,No.3,August,1906, 14 pp., 10pis.

« Bull.M.^C.Z.,Vol. L.,No._4,November,1906,26pp.,4_pis.

»Mem.M.C._Z.,Vol.XXXV.,^No.1,February,^1907,20pp., 15pis.

» Bull.M.C.Z.,-Vol. L.,No._6,February,1907,48_pp.,18_pis.

ioMem.M.C._Z.,Vol.XXXV.,^No.2,August,1907,56_{pp., 9}pis.

»Bull.M.C. Z.,Vol.LI.,No.6,November,1907,22_pp.,1 pi.

u_Bull.M.C.

Z.,Vol.LIL,^No.1,June,1908,14_pp.,1 pi.

MBull.M._{C. Z.,}Vol.LIL,^No.2,July, 1908,8 pp.,5_pis.

M Bull.M.C._Z.,Vol.XLIIL,^No.6,October,1908,285pp.,22_pis.

" _Bull.M.C.

Z.,Vol.LIL,^No.5,October,1908, 11 pp., 2pis.

isMem.M.C. Z., Vol.XXXVII.,February,1909,243pp.,48_pis.

mMem.M.C._{Z., Vol.}XXXVIIL,^{No.1,June,1909,172pp.,5pis.,3maps.}

i 8Bull.M.C._Z.,Vol.LIL,^No.9,June,1909,26_pp.,8pis.

isBull.M.C._Z.,Vol.LIL,^No.11,August,1909,10pp.,3_pis.

2*Bull.M.C. Z., Vol.LIL,^No.13,September,1909,48_pp.,4_pis.

JUSJ

Bulletin of the

Museum

of

Comparative Zoology

AT HARVARD COLLEGE.

Vol. LII. No.

13.

REPORTS OX THE

SCIENTIFIC

RESULTS OF THE EXPEDITION TO THE EASTERN TROPICAL

_PACIFIC, IN

CHARGE OF ALEXANDER

AGASS1Z,

BY THE

U. S.

FISH COMMISSION STEAMER "ALBATROSS," FROM OCTOBER,

1904,

TO MARCH,

1905, LIEUT.

COMMANDER

^L.M.

GARRETT,

U.S. N.,

COMMANDING.

XX.

MUTATIONS IN CERATIUM.

By Charles Atwood

Kofoid.

With

Four Plates.

[Publishedby ^PermissionofGeorge M. Bowers,^{U. S.} Fish Commissioner.]

CAMBRIDGE, MASS., U.S.A.:

PRINTED FOR THE MUSEUM.

September, ^1909.

No.

13.

— _{Reports of}

the ScientificResults

of

^the

Expedition

^{to the}

Eastern Tropical

Pacific,in

charge of Alexander

_Agassiz,

_hy

the U. S.

Fish Commission Steamer "Albatross" from

October,

1904,

^to

March, 1905, Lieut. Commander

L.

M. Garrett.

U.

S. N.,

commanding.

XX.

Mutations

in

Ceratium. By ^Charles Atwood Kofoid.

CONTENTS.

Normal_schizogonyinCeratium ^. 213 Division of ancestral skeleton . 214 Formation of new skeletal

parts 214

Similarity of normal schizonts

inchain . 215

The

genus Ceratium 217

Tripoceratium,subgen. nov. ^. 218 Macroceratium, subgen.^{nov. .} 218 BiceratiumVanhoffen ^{. . .} 218 Amphiceratium^{Vanhoffen . . 219} PoroceratiumVanhoffen ^{. . .} 219

The

mutation of Ceratium _tripos

toC.californiense

....

²²⁰

Chronology and nomenclature of skeletal parts ofchain ^. . 220 Genuinenessofthechain . . 221 Completeness^ofthechain . . 223 Evidenceofmutation

....

²²⁴

Progressive perfection of the mutant

...

²²⁵

Significance of autotomy and

resolution of the C. _tripos

skeleton 226

The

mutation between Ceratium californienseandC. ostenfeldi 227 Evidences of genuineness and

completeness 228

Earlier observations on mutations

inProtista 229

MutationsinDiatoms

....

²²⁹

MutationsinDestnids

....

²³²

MutationsinCiliates

....

²³²

MutationsinCeratium ^{. . .} 233 Significance of thephenomenon ^{. 235}

Unknown

factors 236 Seasonal polymorphism (Gran

and

Lohmann)

²³⁷

Gamete_hypothesis 244 Degeneration ^or atavism _hy-

pothesis 245

Mutation hypothesis

....

²⁴⁷

Bibliography 253

Explanationof Plates

Normal Schizogony

in

Ceratium.

Throughout

^the

genus Ceratium

asexual reproduction occurs, ⁱⁿ so far as is

known,

exclusively

by

schizogony. Multiple spore formation

such

asis seen in

some

other genera ^ofdiuoflagellates, as for

example

bulletin:

in Pyrophacus, ^{is, as} yet, entirely

unknown.

This schizogony ^{takes the} form of

an

_obliquefission of the entire organism

whereby

not only the

nucleus

and

^cell

plasma

^{aredivided but the}parental skeleton ^{as well.}

Division of Ancestral ^Skeleton.

Thisskeleton is

made _up

of adefinite

number

_{of plates} with_{a typical}

arrangement

throughout ^all the _species of the genus. It is parted ^at schizogony along existing sutures

between

_{the plates}

by

^thefission plane

which

isoblique^to the majoraxis, passing ^atan angle ^ofapproximately 45° from theright anterior shoulderofthe

midbody

^{tothe left} posterior region ^at the outerside ofthe base ofthe left antapical horn.

By

^this

process the ancestral skeleton is parted (see plates 1

and

₂₎ so that the anterior schizont receives apical plates 1—4', precingulars 1"

and

2", the

two

_{girdle plates}

between

the proximal

end

of the girdle

and

a point near the middorsal _line,

and

postcingular plates l'"-3'", in all 9 plates together with ^the proximal ^{half of} the _girdle and anterior moiety^of the so-called ventral _plate.

The

_posterior schizont receives precingulars 3"-4", the twogirdle plates

between

itsmiddorsal

gap and

^itsdistal end, postcingulars ^4'"

and

5'"

and

_antapicals 1""

and

2""; ^inall 6 _plates, the distalhalf ofthe_girdle

and

the posteriormoiety ^ofthe ventral"

plate."

The

ventral _plate, as Lauterborn (1895) has shown, ^is divided

between

the

two

schizonts

by

^a

more

or lessoblique line,

which

_passes from the flagellarpore ^atthe proximal

end

ofthe girdle ^tothe attachment areaat its distal end.

The

_positionof the fission plane with ^{reference to the} skeletal plates

was

_{correctlygiven}

by

^Biitschli (1885)

and Bergh

(1886).

butthe

number and

position of the platesare not completelyor correctly given

by

^{either author.}

The

_plates

_composing

the skeleton

and

the nomenclature here used were described

by me

ina recentpaper (1907b).

Formation

_{of Neiv}Skeletal Parts.

As

theschizonts diverge^{after nuclear} division, their exposed

plasma

adjacent ^to thefission plane ^is

moulded

into the form of the completed epitheca and

hypotheca and

^iscoincidently reclothed with a thin hyaline pellicle,

which

ina short time

shows

the _pores

and arrangement

^ofsuture

lines

and

plates characteristic ofthe_species.

The newly formed

^skeletal

parts, as I

have shown

elsewhere _(1908), take

on

the facies of the pa- rental individual_; thatis,ifthe parental skeleton

was

of acoarse-ribbed

and

rugose type ^{or ofa}

more

delicate

and

_hyalinecast, the

newly formed

plates ofthe daughterschizont are speedily thickened

and

their surface

kofoid: mutations

in

ceratium. 215

diversified to adegree corresponding^to that of the parental skeleton

by

a sort of

compensatory

growth.

The

whole _process isa relatively rapid one, with theexception ^{that the} prolongation ^of the apical horn to the

full length

normal

tothe isolatedindividualis often delayed^{as inall the} individuals, save the anterior one_only, in achain of C. vultur

shown

in plate 4, fig. 7.'

The

result of this normal _{process of} schizogony ^is the formation of schizonts

which

are, in all essential details, of similarform

and

structure.

An

illustration ofthis

phenomenon

^{is seen in thischain}

of_{C. vultur,}

where

aseriesof schizonts of at least thefifthgeneration^are seen still inchain. All exhibit the

same

form of

midbody,

essentially similarspread^ofhorns withlike

major

^flexuresneartheir bases.

The

cell wall even ofthe youngest^{skeletons is}thickened to alike extent

and

in

homologous

regions,

and

all of the anterior horns

have

lateral _lists, as does the ancestral skeleton seen in the epitheca^of the anterior schizont.

Similarity of

Normal

Schizontsin Chain.

The

differences

between

thecells in a

normal

chain consist of varying lengths^of the _apical horn (though ^thisis often surprisingly uniform)^; differencesin thelength ^oftheantapicals, which in the case ofvery ^long-

horned

_species,suchas C. carriense, are often considerable; differences in the

major

^flexuresor spread ^{of the} antapical horns _{resulting possibly} fromjuxtaposition ⁱⁿ chain _formation,

and

slight differencesⁱⁿthe text- ure oftheskeleton

and

_{the degree}of

development

^ofribs

and

lists

upon

its surface arising during the _{rapid process} of

compensatory

growth.

Most, ^if not indeed _all, of these differences fall either in the category of

growth

^or agedifferences or individual fluctuating variations.

When

measured and

plotted, theirdimensions

form

a

normal

_frequency^{of error} curve. I

have made

such

measurements and

_plotsfor a

number

of the species of

Ceratium on

ten toa thousandindividuals,

and

findthat these differencesconformtypically totheso-called fluctuatingtypeof variation.

The

chain of C. vultur(plate 4, fig. 7) ^isafair representative ofthe usual degree of variation. I

have

found ashigh ^as

twenty

individuals inchainof this species,

which

isone prone ^tochain _formation, with

no

greater variation

than

that

shown

here.

Extremes

of variation in indi- viduals in chain are to be seen in Pouchet's (1894, p. 171, fig. 13) figures of chains of 3

and

4 schizonts, but even here the differences are strictlyofthekinds above mentioned.

In sharp ^contrast with

most

Protozoa _{(notable exceptions} appear ⁱⁿ linear arrangement ^ofrecent schizonts of Spirochaeta and

Trypanosoma)

and

even

most

of the dinoflagellates, the schizonts of

Ceratium

have a

216

tendency,

more

orless pronounced,^toadhereinchainfor

some

timeafter schizogony. This tendency ^is

more marked

in

some

_species than in others.

For

_example, in the

subgenus Euceratium Gran

^{in the} species C. vultur, C. schranki, ^C. carriense,

and

C.

palmatum,

^{chains of}

4-20

individuals arenot unusual,^whileinC.furca, C.fusus, C.biceps,

and

other representatives of the subgenera Biceratium

and Amphiceratium

rarely

more than two

individuals (except in C. candelabrum) ^areseen in chain

and

chains are relatively infrequent.

Chain

formation is

most

_readily found incollections

made

in the night ^orin the _early morning.

In my own

_experienceat

San Diego

(latitude 32° _40') they ^are

most abundant

in collections

made between

3

and

7 o'clockin themorning, ^celldivision seeming^to be favored

by

^the conditions of illumination

and

_possibly

by

the_fallingtemperature prevailing during the night.

The

schizonts part

company

shortly ^after the completion ^of schizogony

and

skeletal forma- tion,

and

chains areabsentorrelativelyrarein collections

made

laterin the day.

The _morphology

ofchain formation is correlated with the presence^of

an

_{apical pore}at the

end

of

an

apical horn.

As

the

new

skeletal moie- tiesare

formed

respectively on the _posterior

and

anterior regions ofthe divergingschizonts,the

plasma

^oftheposterior

member

is

drawn

outina long ^strand

which becomes

the _apical horn. Its tip restsimmediately

upon

^{the distal}

end

of the

newly

forming girdle (plate l), at

which

point the

plasma

^{of the}

two

individuals remains in continuity without interference

by

the forming ^skeleton.

As

the

newly

forming ^skeletons are completed, the apical pore ^ofthe posterior sehizont ^isset

under

the anterior shelforlist of thedistal

end

ofthe girdle ^at the

margin

^ofthe ventral plate (plate l) of the anterior sehizont.

The

_posterior ^{list of} the _girdle isnot

formed

at this point,

and

_{the apical} horn asit passes posteriorly ^{lies in} a channel or depression on the ventral face of the

midbody

along the _right

margin

^{of the ventral} plate.

The

_place of junction

on

the anterior sehizont I designate as the attachment area (att.a.)

and

the depression^as the chainchannel _{(ch. ch.).}

The

anterior

end

ofthe apical hornisalsomodified,^itsventral sidebeing prolonged ⁱⁿ a short _lobe, giving ^to the _apical pore

an

irregularly oblique opening (Entz, 1905), a conditionfound inindividualsin chain

and

also in those but recently released from chain formation. In

most

free individuals the _apical pore^is transverse, as ⁱⁿthe anterior parental skeleton of the sehizont I₃in the chain

shown

_{in plate} 1.

In the course of

my

investigations

upon

^the dinoflagellates of the Pacificconducted forthe past eight years ^at the

San

_Diego station

and

kofoid: mutations

in

ceratium. 217 upon

the collections ofthe "

Albatross^" in the _tropical Pacific

and

else- where,

many

^{instances of chain formation}

^{have come under} my

^obser-

vation.

They

^have always been of interest

and have

received close inspection,

and many

^{arerecordedin}

my

unpublished sketches, especially those having

any

bearing on the question of variation in Ceratium.

Hundreds

ofsuchchains have been _inspected

by

myself^or

my

^assistant,

Miss Rigden.

With

theexception ^of three instances noted later these chains

have

been of the

normal

_type described above.

The

material

examined

from

San Diego

^{coversall seasons of}the year

and

_depths

from 0-500

_fathoms,

and

thatfrom the

"Albatross"

includes collectionsfrom

Alaska

waters, the coast of California,

and

from the Expedition ^to the Eastern

Tropical ^Pacific extending

southward

to Easter Island in the

South

_Pacific,

and

from depths^of

0-800

fathoms.

My

^{material is there-}

fore _fairlyrepresentative of

Ceratium

in its oceanic

and

neritic environ-

ments

within the range of conditions of the

normal

distribution of the genus.

The

literatureof the subject prior ^to

1908

contains but fewreferences to chain formation

beyond

^{those Qf Michaelis} (1830),

Allman

_(1855),

Murray

(1882),

Pouchet

(1883, 1885,

and

_1894), Btitschli (1885),

Bergh

(1886), Schtitt (1895, 1896), Karsten (1905, 1906, 1907),

and Entz

(1907).

In

all these cases the type ^of chain formation isthe

normal

one above described.

The Genus Ceratium.

The

_genus

Ceratium

isalargeone ofwide distributioninthe plankton of fresh water

and

the sea.

Most

of the _speciesare also ofwidedistri- bution

and some

are cosmopolitan.

They

^{exhibit a wide} range ^of variation in

many

^{cases, especially in length}

^and

differentiation of the horns, their principal organs ^of flotation, in adaptation ^to varying conditions of^life.

No

less

than 290

different

names

havebeen given ⁱⁿ thisgenus ⁱⁿrecognition of the_species,subspecies,

and

othersubordinate categories ⁱⁿ

which

the forms have been classified. In the opinion ^of the writer probably not ^less than

two

thirds of these are based

upon

growth,age,ortemperaturecharacters, whilethe remainingthird are well

founded

; but even so, the degree ^to

which

the _{biological process} of speciation has progressed ^{in this} genus ^{is, in} comparison with other dinoflagellates, except Peridinium, relatively great, a fact of possible significance ⁱⁿ connection with the

phenomenon

^{of mutation herein}

described. All of the _{species of}the _genus, with the _possibleexception

218 BULLETIN

of a few numerically ^rare

and

structurally widely divergent species, ^fall into five sharply

denned

_subgenera asfollows:

—

Tripoceratium,

subgen.^nov.

Antapical horns subequal, reflected anteriorly, theirtipssymmetrically pointed closed. Apical horn differentiated abruptly from ^the rotund midbody. Post- margin rounded, no postindentation. Over25 _species. C._tripos, C. arcuatum

(fig- A).

Macroceratium,

subgen.^nov.

Antapicalhorns, subequal, reflected anteriorly, theirtipstruncate, open, orcon- tracted or rounded, butusually with terminal pore. Apical horn differentiated abruptlyfrom moreor less rotuud midbody. Bases of the antapicals projected more or lessposteriorlybeyond midbody forming ^a postindentation. Over 25 species. ^C. macroceros, ^C.gallicum (fig. B),

C

vultur (plate4, fig. 7).

Biceratium

^Vanhoffen.

Antapical hornsmore orless unequal, deflected posteriorly, theirtips pointed, closed. Apical horn differentiated or tapering from the midbody.

Deep

post- indentation. Over10 _{species. C-furca,} C.pentagonum (fig. C),^C.californiense

(plates1-3, plate4, fig.4).

Fig. A. Ceratium arcuatum, dorsal view.

X

^155.

Fig. B. C. gallicum,ventral view.

X

^155.

Fig. C. C.pentagonum,dorsal view.

X

^155.

KOFOID: MUTATIONS

IN

CERATIUM. 219

Amphiceratium

^Vanhoffen.

Autapical horns^directedposteriorly, theirtipspointed, closed; the rightminute or suppressed, the^leftandtheapical greatly elongated. Midbodyusuallygrad- uallymerging^intotheapical horn. Several_species. C.fusus.

Poroceratium

Vanhoffen.

Antapical hornssubequal, directed posteriorly. Midbody^extendsto apical pore.

Apical horn notdifferentiated.

A

few_species. C.gravidum.

The

_subgenera Tripoceratiuin

and Macroceratium

_together

form

the

group

designated

by Gran

(1902) ^{as the}

subgenus

Euceratium, but ^it

seems

best to recognize as subgenera the

two

_large natural groups ^of species containedtherein

and

_{easilyseparable}

on fundamental

structural characters.

The

_{C. tripos}

and

C. macroceros sections

have

been _recog- nized in various ways,

though

^{not hitherto as} subgenera,

by

^recent systematists, as, for example,

by

^Ostenfeld (1903), ^Pavillard (1907), Karsten _(1907),

and

Paulsen (1908).

The number and

relation of the skeletal plates are similar^{in all} the subgenera. ^Ihave therefore

(1907

b) considered^{thisfact as}the_justifi- cation forkeeping ^thislarge

genus

intact,since skeletal plates constitute generic charactersthroughout the family Peridinidae,^to

which Ceratium

belongs.

Amphiceratium and

Poroceratiumare

more

aberrant subgenera in

which

the _tripartite

form

of the skeleton

prominent

^{in the othersis} considerably obscured

by

specializations for flotation.

The

other three subgenera, Tripoceratium, Macroceratium,

and

Biceratium, ^{are less di-} vergent

and

notso aberrant.

They

contain the simpler

and presumably more

_{primitive species.}

These

also contain the _{greater part} of the speciesⁱⁿthe genus

and

areseparated

from

one another

by fundamental

structural features, such as the direction

and

curvature of the antapical horns

and

the formsof their distalends,which arenot sopatentlyadap- tive modifications.

Should

these characters alone be usedasa basisfor the subdivision of the genus, ^it

would

necessitate the inclusion of

Amphiceratium and

Poroceratium in the

subgenus

Biceratium.

The

morphological^basis

upon which

^these three principal subgenera ^restis thus of general import throughout the genus.

The

mutationsdiscussed in thispaper connect the ^three

fundamental

subgenera, Tripoceratium, Macroceratium,

and

Biceratium.

Ceratium

{Tripoceratium) tripos mutates to C.

{Biceratium) californiense,

and

220 BULLETIN:

C. (Biceratium)californiense ^isfound inchain with C. (Macroceratium) ostenfeldi.

Both

the amplitude

and

the direction taken intheseabrupt changes ⁱⁿformare of great interest,

and

_{are, I believe,} ofprofound sig- nificance in their bearing

upon

the question ^of the

method

of organic evolutionin nature.

The

_species in or

between which

these mutations occur are well- established species ofthe _genus,

have

a

wide

distributionin the _sea,

and

in the main, excluding questions ^of

synonymy,

^ageneral recognition ⁱⁿ the literature of the _subject.

The

evidenceof this abrupt

change

ⁱⁿ form, this mutation, ^or perhaps

we may

^even say transmutation, ^of species

seems

unequivocal.

The

facts

upon which

these conclusionsrest are asfollows.

The Mutation of Ceratium

tripos to C. californiense.

The

chain _exhibiting this

change

(plates 1-3)

was

taken at8 a.m.

Jan. 24, 1905, ^{at Sta.} 4737, 19° 57'

30"

_S., 127° 20' 18"

W.,

^{on our}

line

between

the Galapagos ^Islands

and Manga ^Eeva

ⁱⁿ

^an

intermediate haul from

300

fathomsto the surface. It consists of fourindividualsin a chain

which

hasresulted from

two

_succeedingcell divisions.

The

four individuals are in the thirdgeneration, that ^{is, are}

granddaughter

^cells ofan _original grandparent^cell.

The

_original skeleton of the grandpar- ent cell is

now

_{widelysevered,} its anterior moiety forming the forward

armor

of the foremost

(uppermost

^{in the} plates) individual,

and

its posterior moiety the rearward ^{shell of} the

hindmost

_(lowermost in the plates) ⁱⁿthe chain.

Chronology

and Nomenclature

_ofSkeletal Parts of Chain.

An

analysis of the chronology of skeletal formation

and

the distribu- tion in the present chain ^of the skeletal parts formed in the threegen- erations is illustrated in the

accompanying diagram

ⁱⁿ

which Aj A

2

A

3

and

_Pj

P

₂

P

_{8 represent} the anterior

and

posterior moieties of the skele- tons formed

on

the _{first, second,}

and

third generations respectively.

For

convenience in referring ^to the individuals in the _following dis- cussion they^are

numbered

from the anterior end posteriorly, with the distinguishing

number

ofthe generation

added

as subscript^;thus the in- dividual I₃ is the first (foremost) ^individualin the third generation,

and

itsskeleton

=-

consists of the anteriormoiety ^{of the}grandparent^{cell of} the chain

and

a posterior moiety

formed

at the latest division. It is

kofoid: mutations

in

cekatium. 221

patent ^that each individual possessesone moiety^ofthelatestgeneration, while theother has descended from

some

antecedent one.

Ii

An

_inspection of the _figures

on

_plates

1-3 and

a comparison ^of the skeletal conditions there presented

makes

it evident that the present chain _reveals,

by

^{virtue of the} existence of fixed skeletal parts passed

by

^"

down

inheritance," the skeletal

morphology

^{for three} generations.

The

chains of

Ceratium

offerthus a unique opportunity ^forthe study ^of pedigree^{cultures in}relatively simple organisms.

The

species characters in

Ceratium

lie mainly ⁱⁿ the skeletal _parts,

and

these are so preserved in latergenerations ^that theskeletal

morphology

^{ofalineofdescent}

may

be traced with a degree of certainty unsurpassed ⁱⁿ other organisms.

The

_geneticconnectionofthe

members

^ofthe chainis insured

beyond

^all question, a condition ^{difficult to realize}

where

the schizonts are separated at theclose ofcell division.

Furthermore

there can be

no

possibility of accidental contamination ofa culture

from

air-borne spores orencysted forms such as

must

_always attend pedigree ^culture

work

with

most

flagellates

and

ciliates.

Genuineness of^the Chain.

This _is,

beyond

^all question, a genuine chain ^of genetically related

Ceratium formed by

schizogony with ^skeletal

and

_plasmatic continuity, asis usual in chain formation. It is not achance assemblage ^{of indi-} viduals, jostled together ^inthe

crowded

collection. Neither is the pos- terior

member

of the seriesaccidentally attached to achain of unrelated origin.

The

_followingfacts sustainthis assertion:

—

(1)

The

chain has held together not only during ^the

more

or less violentdisturbancesinvolved in

making

^a plankton haul with^{a silk}net from a vessel at _sea, but also during ^the microscopical examination in the courseof

which

it has been rotated several timesin freeing ^it

from

entangling organisms

and

in securing dorsal

and

ventral views. It has also survived the changes^{offluid incident to} thestaining process

and

a final transfer

from

a 4per cent solution offormalin inseawater through alcohol grades^to glycerine,

made _by

passing the ^fluids through beneath the cover_glass. In the course of these changes ^it has

been

_subjected

to

some

_bending

and

_strains,

but

has not parted except ^as

shown

(plate 3) ⁱⁿ the _figure of the cell contents,

where

the junction ^{of cells} II8and III₃ ^is slightly disconnected.

(2)

The

connections

between

the _apical horns of II₃, III₃,

IV

8,

and

the

attachment

area at the distalends ofthe girdles of^I3^, II_3,

and

I1I₈,

respectively, areboth

normal and

_typical. I have studied with _especial care under the oil

immersion

lens the detailsof the

most

important con- nection, namely, ^that

between

the apical horn of

IV

8 (Ceratium tripos representative)

and

the cell

(III³

=

C. californiense) ^to

which

it is at- tached anteriorly. This is in all respects perfectly typical, even the protoplasmic bridge appearing ^to be still intact.

(3)

The

_apices of all the horns, save the ancestral one,

which

is

on

theanterior skeletal moiety ^{of I}3, exhibit the _{flaring, slightly} lobed

mar-

gin about theapical pore, described

by Entz

(1905), which ^ischaracter-

istic ofthis part of recently

formed

anteriorhorns.

These

are the con- ditionstobe expected ⁱⁿ a

normal

chain offour individuals.

(4) Contrasts in the

hyalinity

and

porulation of the anterior

and

_pos-

teriormoieties ofthe skeletalwall of the several individuals are indicative of recent

normal

chain formation.

These

differences are

due

to the fact that the skeletal wallgrows darker with age

and

itspores are

more

_easily seen. This is plainly noticeable ⁱⁿthecase ofIII3

and IV

3,

upon whose

recent separation

by

^{division the}

whole

_point of this

communication

rests.

The

anterior skeletal

moiety

^of

IV

_S in the _original specimen ^is very plainly of a

more

delicate texture than the _{posterior one,} barring only theright antapicalregion

which

has apparentlyrecently exuviated or is undergoing resolution.

The

_{posteriormoiety} ^ofIII8 islikewise of a _lighter texture than the anteriorone of that individual,

though

^the difference

between them was

less strikingthan in the case of the

two

regions^of the skeleton of

IV

₈^.

These

contrasts are just such as

would

appear ^if III₃

and IV

8

had

_{recently originated}

by

^{the division of the} posterior

member

ofa chain oftwoschizonts. Differences of similarim-

K0F01D

^:

MUTATIONS

IN CEBATITJM.

223

portcan also be detected

between

the older

and newer

skeletal parts

on

the

two

sidesof the lineof fission in theanterior _pair, I₃and II

3^, ofthe chain.

(5) Finally, the nuclear conditions within the cell

body

(plate 3) ⁱⁿ all four individuals are prophetic^of anotherdivision. It

was

not _pos- sible in the unsectioned preparation^to

make

out finercytoplasmic^struc- tures within the skeletal _wall, but the nuclei have either completely divided

(IV

3) ornearly ^so (III³) or are plainly ⁱⁿthe process of division (II3

and

I

3).

The

division stages here

shown

are similar to those

which

Lauterborn (1895) has found in C.

MrundineHa,

^a fresh-water species,

and

are in all respects ^of the

normal

_type.

There

is an _ap- parent progression ⁱⁿ the _stage of mitosis from the anterior schizont posteriorly.

1

No

structural feature is apparent ⁱⁿ the individualcellsto which this difference in mitotic activity can be traced.

There

is,forexample,

no

corresponding^series of differences in

volume

of thecell mass, ^orinratio ofnucleus

and

_cytoplasm. It is possibly of interest ⁱⁿ this connection to note thatdivision has progressed ^{farthest in}the _posteriorcellsof the chain, those

which

in

normal

locomotion are bathed in water

which

re- ceivesthe waste products ^ofthe

more

anteriorly located

members

of the chain.

Locomotion

occursin chains of

Ceratium

even during division, forthe_{flagella persists}during theprocess ofschizogony(see Lauterborn, 1895). ^I

have

myself seen chainsⁱⁿ locomotion with active flagella in recently collected plankton,quite contrary^{to the}observationsof

Murray and

Tizard (1882).

Completeness of ^the Chain.

Not

_only^isthis agenuine chain,but itis in all probability acomplete chain.

The

_presence of along^anterior horn with _squarely truncate _tip

upon

^{the foremost cell ofthechain is conclusive evidence that the chain}

is complete ⁱⁿ that region, that is,that

no

schizonts havecut loose from the chain atthis

end

_{during the} present cycle of schizogony.

The

_tipof all

young

apicalhorns is

peculiarly asymmetricalⁱⁿ adaptation ^to chain

1 Inview ofthe

many

discussions over the direction of the plane of division

among

flagellates,especially ⁱⁿ parasitic forms such as Spirochaeta and Trypa- nosoma, ^{it is of interest to note} here that during the process of mitosis the equatorialplane^orcleftbetweenthe partingchromatin massesshiftsfrom _approx- imatelya longitudinal position toone at 45° to themajor ^axis.

The

_seemingly

oblique division of the dinoflagellates^isthusinits relation tothe position of the nucleus_priorto mitosis, a longitudinal one. ^Itis,however, obliqueⁱⁿthe skeleton andalsointheplasma, ^{unless thelattershifts}with the nucleus.

BULLETIN:

formation.

The

fact that the _antapical hornsof the

hindmost member

ofthechain have

undergone autotomy

^{is also} suggestive that this

end

of thechain is likewise complete.

As

I have

shown

elsewhere _(1908),

autotomy

^occursnot infrequently ^inisolated

Ceratium

in theplankton, but 1 have never seen it in

Ceratium

in chain.

Autotomy

possibly occurs only under ^conditions unfavorable to

normal

cell division. Be- causeofthis

autotomy and

^the characters ofthe posterior skeletal

moiety

P

2, I regard the posterior

end

also ofthe chain ascomplete.

It is a fact,

which

I

have

_frequently observed in

crowded

_plankton

collections, that the dinoflagellates,

Ceratium among

them, ^often tend to celldivision (often abortive) tinder the adverse conditions

presumably

prevailingⁱⁿsuch collections. Itseems improbable, however, that ^this division approaching ^{in the} chain

shown

in plates

1-3 was

_brought

on by

^{the treatmentto}

which

_they

were

_subjected in the _{process of} collec- tion, for ^{it is}far

advanced

in division,

and moreover

it

was

our

custom on

the

"Albatross"

_Expeditionto fix the catches of the fine silk nets very shortly ^after they were brought aboard, ^after a brief preliminary treatment with chloretone.

Evidence of Mutation.

.Turning

now

to a detailed consideration of the data afforded

by

^the chain

shown

in plates 1-3,

we

find that it consists of four individuals, the rearmost of

which (IV

3) is

Ceratium

_tripos or a closely related species belonging ^{to the}

subgenus

Tripoceratium, ^while the other three belong ^to the

subgenus

Biceratium, to a species

which

I have _recently

(1907

c), described as C. californiense.

The

characters

which

deter-

mine

the _species inquestion ^{lie in} the

main

in the _posteriorpart of the organism.

The

anterior moiety ^of the skeleton contains here

no

_easily recognizable specific characters. It is

impossible ^to determine with certainty the _species of the rearmost

member

of the _chain, since its antapical horns

have undergone

autotomy, the right

horn

having been severed

by

^{a section} plane ^{close to}the

midbody and

^{the left at adistance} of 0.5 ofatransdiameter _(atthe _girdle) from the

midbody.

^{This entire} or_partial removal of the antapical horns obscures in thisindividual the species characters

which

in the subgenus Tripoceratiumare largely found inthe curvature

and

position of these horns.

There

is

no

_doubt,

how-

ever,that the _posterior moiety^ofthe skeleton ofthe rearmostcell

(IV

8) isthat of the Tripoceratium type.

The

_species

was

probably one with broadly evenly curved horns such as C. arcuatum, ^G. schranki, ^if not

kofoid: mutations

in

ceratium. 225

indeed G. tripos ^(&. str) ^itself. It will suffice for present purposes ^to designate ^it as C. tripos.

The

other three

members

of the chain areof a different type.

The

differences lie in the following characters ^: (1)

The

antapicals are un- equal, (2) posteriorly directedwith

some

lateral curvature,

and

₍₃₎ the apices except ^{in II}3 taper to sharp tips. (4)

There

results from the posterior direction of the horns a deep postindentation with sharply defined rectilinear postmargin. In _{C. tripos (cf. Fig. A),}

on

the other hand,antapicals are curved_anteriorly toa direction subparallel ^to the apical

and

their_tipsare abruptly pointed.

There

is

no

postindentation,

and

the postmargin^is broadly curved with

no

_sharp limits.

The

differ- ences

between

the

two

_typesareprofound

and

coincide with the distinc- tions

between

the subgenera Tripoceratium

and

Biceratium.

The

three forward

members

of the chain I₃, II₃

,

and

III₃ belong ^to the _species G. californiense. Incell II₃theantapicals are distallycurved outwardly a little

more

than in I

3

and

III_3,

and

the _tip of the right ^is bluntly

rounded and

that of theleft abruptly pointed, but not in the C. tripos fashion witha

median

symmetrical point, but withasharp point at the outer margin, ^{a feature} found in

many

^other species of the subgenera Biceratium

and Amphiceratium,

^{but not in those of} Tripoceratium.

The

_species

Ceratium

californiense

was

_originally described

by me

(1907) from ^the waters ofthe Pacific off

San

_Diego. Itoccurs through- out the eastern tropical Pacific in the material of the ^"Albatross^"

Expedition. ^It has also been recorded

from

the Indian

Ocean by Karsten

_(1907). It is in

my ^own

experience ^a relatively rare species, occurring sparingly ⁱⁿ the plankton.

There

are

many

^such species ⁱⁿ the differentsubgenera ^ofCeratium.

The

_species

C

^. _tripos

and

C. osten- feldiare, however,

common

_{species of} wide distribution inall seassave

polar waters.

Progressive Perfection of ^the Mutant.

The form

of individual II₃isof great interest

and

possibly of consid- erable significance.

The

wider spread ^ofthe horns

and

the absence of the tapering tip bring ^{thisindividual}

somewhat

nearer than ^I3

and

II I₃ to the ancestral type,

though

^{neither curvature nor} tip ^is like that of C._tripos. It looks as

though

^therewere

some

subtile ancestral influence

which

at the first division _(Ix to

^T") tended,

though

^unsuccess- fully

on

the whole, ^to prevent ^the complete ^saltation

from

C. _{tripos to} G. californiense.

Two

generations (asexual!) are here required ^to per- fect the mutation.

The

relations ofthis

phenomenon

^{arebest understood}

when

one recon- structs the

two

antecedent generations from ^{their skeletal} parts ^dis- tributed in the third. This can _readily be

done by

^a comparison ^of the formula on _p. 221

and

_plates

1 and

2.

The

ancestral individual of the chain

was

a G. tripos with skeletal parts

A

1

and P

_x

now on

individuals I

3

and IV

₃. Its daughter ^cells were I₂

and

II₂, the first

with skeletal parts

Ai and P

₂, the second with

A

2 and

P^ ^Thus

^the

anterior

member

_(I2) ofthe chain with

two

individuals

had

the anterior moiety

(A^

^ofthe original C. tripos skeleton

and

a

new

_{posterior moiety} (P²)

which was

fundamentally ^of the Biceratium _type, but the

newly formed

skeletal parts

were

still subject ^to a lingering influence that

shows

unmistakable relations to the ancestral Tripoceratium type. In the next _division, in which I₂ forms

—

_,

and

II₂ forms

=-^, ^the

I-L3 ^-l' 3

newly formed

posterior moieties (P3 in I₃

and

III₃

) attain the _typical form of C. californiense while

P

₂ is passed^{to II3.}

The

_posteriorskeletal moieties containing ^the

most

_clearly defined subgeneric

and

_specific characters_Pi,

P

₂,

and P

3thus

form

a shortseries with the

most

_abrupt change

between P

x

and P

2

and

record acomplete transformation ⁱⁿ the short space of three generations (two ^cell divisions),

from

the _species C. tripos to the species C. californiense,

and

from the subgenus Tripo- ceratium to the

subgenus

Biceratium.

The

chain

shown

in plates

1-3 was

discovered in material preserved in formalin. Its further

development had

^{been stopped in the very} act of a third division.

What _might

have resulted from this division cannot be told.

The

^fact that three of the four daughter ^{cells areof} the type ^{of C.} californiense

and

that the

two

generations

show

a

move- ment

in thedirectionof the _perfectionofthattypesuggests ^its probable continuance.

Significance of

Autotomy and

^{Resolution of the C. tripos Skeleton.}

The

condition of the skeleton of the C. tripos cell, especially of its posterior moiety

P

₁₅ isalso

most

suggestive.

Not

_only

have

the horns

undergone

autotomy, but ^{there is} evidence that the skeleton is being further modified.

The

^{wall of the left} _antapical

^{horn and}

that of the right antapical region (Plate2) ^isexceedingly thin

and

_tenuous,

and

the pores are scarcely^visible, as

though

^{the wall}

had

been thinned

down _by

a_process of solution. This condition is in sharp contrast to that ofthe unmodified ancestral skeleton in therestofthe _posteriorskeletal moiety Pi. This hasa heavier, ^less hyaline wall

whose

_pores

become

_gradually

KOFOID

:

MUTATIONS

IN

CERATIUM. 227

fainter in the

more

distal parts. It thus appears ^{that the ancestral} skeletal moiety, ^{i. e.}of G.tripos, of this posterior

member

^of the chain

is gradually disappearing. In all other structural features

and

in the process ^{of cell} division this

member

of the chain appears^{to be a}

normal

cell.

The

_{question naturally}arises, will this process continueuntil the old skeleton is entirely^lost

and

will a

new

skeleton ofthe C.californiense type be

formed

in its place¹ This cell

IV

3isa sister cell of a C. cali- fornienseIII₃^. Is not its inherited skeleton of the C. tripos type,

and

areits nucleus

and plasma now, and

perhaps ^since the first division, of the C. californiense type

1

?

Only

pedigree ^cultures can _give a decisive

answer

to these interesting questions.

The Mutation between Ceratium

californiense

and

C. ostenfeldi.

Plate

4, Fig. 4.

Another

chain

was

taken in the intermediate haul

from 800

fathoms to the surface at8 a. m. on

December

31, 1904, at station 4711, ^{7° 47'}

30"

_S., 94° 5'

30" W., on

^{our line}

between

Easter Island

and

the Galapagos ^Islands.

The

chain consists of

two

individuals only.

The

anterior

member

ofthe chain is a Ceratium, ostenfeldi, the posterior ^is C. californiense.

The

anterior

member

has the _antapicalhorns recurved anteriorly with truncated

open

^{tips. Their bases are also projected}

posteriorly, forming ^a deep postindentation

and

a long straight post- margin.

These

are characters of the

subgenus

Macroceratium.

The

posterior

member

has the _antapical horns _projected posteriorly, with slight

outward

curvature, a characteristic of the species (C. californiense), with tapering pointed tips

and

_deeper postindentation, characteristics ofthe subgenus Biceratium.

The

mutation here involvesthe two_species C. ostenfeldi

and

C. californiense, belonging ^to

two

of the important subgenera ^{of the} genus,

Macroceratium and

Biceratium.

The

anterior cell of this chain has the characteristically

open

tips of the

subgenus

Macroceratium.

The

_extruding

plasma

(plate 4, fig. 5) leaves

no doubt on

this point.

The

_typical proportions^{ofthe three}horns

and

the general habitusofthe cell suggest ^{that it is a}

normal

_cell, not

an

auto- tomizedone.

Owing

^{tothestate of}

development

ⁱⁿ

which

the _relatively short horns of the anterior

member

of this chain appear, ^its specific identity ^is

somewhat

obscured. I

have

referred thecell to the _species C. _ostenfeldi rather than to C. macroceros, because of the distance to

which

_{the major} ^{flexures in the} bases of the antapicals are projected posteriorly. This is

much

_greater in C. macroceros

and much

less in