CRUSTACEA

34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 mating the male chelonethid attaches to the supporting surface be-

VII. CRUSTACEA

The

crustaceans,by comparisonwith theprogoneatearachnidsand diplopods or withthe opisthogoneate chilopodsand hexapods, might besaid to be ^"mesogoneate^", inasmuch as the genital openings are onthe intermediatepart of thebody.

However,

ifthenumericalposi- tion of the segments is considered, the genital segment of

some

of the

many-segmented

branchiopods

may

be as far behind the

mouth

as that of the chilopods,and considerably to the rear of the genital segments of insects.

The

segmental position of the gonopores is highly variable inthe Entomostraca, butin thisgroup theapertures arealwayson corresponding segmentsinthe

two

sexes;intheMala- costraca the genital openings are fixed with specific segments, but they arealwaysondifferentsegmentsinthemale andthe female.

To

enumeratethepostoraltrunksegmentsof theCrustaceaincon- formity with the enumeration followed in the Chelicerata,

we

must beginwiththesomite of the secondantennae,which morphologically correspondswiththatof the chelicerae.

The

gonoductsof the Entomostracausually openseparately tothe exterior;in

some

cases thegonoporesareonthe limb-bearing thoracic region of the body, but

more

generallythey occur on the abdomen.

Intromittent organs are present in

some

groups, as in Branchiopoda and Ostracoda, the males of which

may

havea pair of penes, or a singlepenisthroughwhich bothvasa deferentia discharge.

Examples

of the paired type of organ are

shown

here in

two

branchiopod species,Branchipus serratus (fig. 14A,

B)

and Polyartcmia haseni (C).

The

two penes of the first species are short, thick papillae (A,

Pen)

projecting ventrally from theundersurface of thesecond

NO. 14 INSECT

ABDOMEN—

SNODGRASS 39 abdominal segement (somite

XXVII),

but provided with muscles arisinginboth thesecondandthefirst segment.

Each

penisis

armed

distallywithahook

(B) mesad

of which isthe gonopore. InPoly- artemia haseni thepenes (C,

Pen)

arelong tubularorgansprojecting posteriorly

from

theundersurface of thefirst and second abdominal segments, which in this

form

are somites

XXI

and

XXII. The

branchiopods, except in cases of parthenogenesis, propagate by sex

Pen

Fig. 14.

—

Crustacea-Branchiopoda-Anostraca: showing variable position of penes.

A, Branchipus scrratiis, with penes (Pen) arising_on somite XXVII. B, same,end viewof penes and gonopores (Gprs).

peneson somiteXXII.

C,Polyartemiahaseni,with

mating, and the spermatozoa are said to be discharged by the male directly into the genital openings of the female; few observations, however, have been

made

on the exact

manner

of copulation and intromission.

The

Malacostraca have a highly standardized body segmentation, there being,with few exceptions, 18 somitesbetweenthe

mouth

and the telson.

The

trunk is consistently differentiated between seg- ments

XII

and

XIII

into a cephalothoracic regionand an

abdomen

;

but thedistinction between headand thorax is often

somewhat

con-

40 SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95 ventional,and

when

thereisawell-markedanatomical separation the boundary is not the

same

in allcases. Carcinologists usually define the ^"thorax^" as the body region

composed

of the eight segments between the second maxillary somite

(IV)

and the first abdominal somite {XIII),butin

some

cases theheadincludes thefirstof these segments.

The abdomen

contains six somites and the telson, except in one order, the Leptostraca, in which there are seven abdominal somites.

The

genital openings of the femaleare situated always on the sixth thoracic segment (somite

X),

those of the male on the eighth (somiteXII). In

some

cases thegonoducts of the male have a single

median

opening.

The

female generally is provided with a

sperm

receptacle,which

may

be amedian pouchof the ventral integu-

ment

of the thorax, or paired sacs attheendsof the oviducts.

The

gonadsof the Malacostracaare tubular orsac-shaped organs, sometimes lobed orbranched, lyingin the dorsal part of thethorax andabdomen,orrestricted tothethorax(figs. 15G,16 C, 17 C, 18E).

In thedecapods the gonads of oppositesides are generally

more

or less united ^(figs. 17 C, 18E).

The

germinalcellsusuallyoccupy one wall of thegonad,

from

whichthe oocytes orspermatocytesare pro- liferated into the

lumen

(fig. 15

E)

; the cells of the opposite wall (NrCls)

may

have a nutritive function. InAnaspides, as described by Smith (1909), the mesal walls of the ovaries are produced into long seriesofdiverticula, inthe apices ofwhichare located the ger- marialcells, the organs thus resembling the ovaries of insects.

The

gonoductsareeitherstraightor coiled,andgenerallyopendirectly to theexterior,butintheBrachyuratheoviductsendinlarge ectodermal

sperm

receptacles (fig. 18

H,

Spt).

The

gonopores of male Malacostraca are located typically on or close tothe mesalsurfaces of the coxopodites of the lastpereiopods (thoracic appendages), though they

may

lie on the sternal surface betweentheappendages (figs. 15D, 16A, Gprs). Usuallyeach aper- ture is situated on the extremity of a small papilla or tubular out- growth of the integument (figs. 16 B, 18D, Pen), called a penis thoughitisnot the actual intromittent organ. In

some

cases thereis asinglemedian penis arising

from

the venter of the eighth thoracic segment (fig. 16D, Pen), whichcontains a

common

outletduct re- ceiving the

two

lateralgonoductsatitsbase. Ifdirect internalinsemi- nation of the femalefromthe penes, orpenis,of themaletakes place inanyof the Malacostracaitisof rare occurrence, andhas notbeen observed.

With

themajorityof theMalacostracathe

sperm

(or sper- matophores) are placed by the male in the oviducts or in a sperm receptaculumof the female,but theorgansthat accomplishtheintro-

NO. 14 INSECT

ABDOMEN

SNODGRASS 41 mission are usually modified parts of the first, or the first and the second, pleopods (abdominal appendages). In

some

cases, however, the spermatophores are merely attached tothe under surface of the bodyof the female. Fertilizationof the eggs takes place^eitherwithin the oviducts, orinabrood pouchontheundersurface of the female's body.

A

few examplesof the external genitalia of the Malacostraca

Fig. 15.

—

Crustacea-Malacostraca-Syncarida: male genitalia of Anaspidcs tasmaniae.

A, B,appendagesoffirstandsecondabdominalsegments, ventral view,show- ingmesal processes, orgonapophyses (probably the endopodites),thatcompose the intromittent organs. C, left gonopods, posterior (under) view, showing functionalrelation ofgonapophyses. D, ventral surfaceof lastthoracic segment, with gonopores. E, cross-sectionof testis. F,spermatophores. G, testisand vasdeferens. (E, F,

G

fromSmith, 1909.)

Endpd,endopodite;Expd,exopodite;lijon,2Gon,^firstandsecondgonapoph- yses (probably endopodites); Gprs,gonopores; NrCls,nutritive cells of testis;

Prtpd, protopodite; Spc, spermatocytes; Sps, spermatozoa; Stn, sternum

;

T,tergum;Tcs,testis;Vd,vas deferens;XII, XIII.XIV,twelfth, thirteenthand fourteenth postoral somites.

will suffice to illustrate the general structure and ^variations of the organsin thisgroup.

The

typicalstructure of the externalgenitalorgans ofmaleMala- costracaiswell

shown

in the Anaspidacea. In Anaspides tasmaniae themale gonoporesare

two

obliqueslits on the venter of the eighth thoracicsegment (fig. 15D, Gprs) situatedonoval elevationsbetween thebases of thelastpairoflegs.

The

functional intromittentorgans

42 SMITflSONIAX

MISCELLANEOUS

COLLECTIONS VOL. 95 are

composed

of

two

pairs of long processes arising

from

the inner ends of the basal segments*of the first and second pleopods, which are, therefore,probablytheendopodites of theseappendages (A, B,

Endpd). The

genitalprocesses,orgonapophyses,of thefirstpair

(A)

are expanded distally and hollowed on their inner surfaces; those of thesecondpair

(B)

arecylindrical,andtheir distalendsfitsnugly into the concavities of thefirstpair (C).

By means

of theseorgans the male during mating inserts a pair of large, horseshoe-shaped spermatophores

(F)

into a two-branched receptacular pouch open- ing on the venter of the last thoracic segment of the female.

The

spermatophores are probablytaken

from

the gonopores of the male intothecavitiesof thefirstgonapophyses,and forced

from

thelatter bythe secondgonapophyses. Withinthe receptacularpouches of the femalethespermatozoaaredischarged

from

thespermatophores,and thelatter arethenrejected. Since thereis evidence that fertilization of theeggstakes placeinthe oviducts,itissupposedthat thesperma- tozoa are transferred into the openings of the latter on the sixth thoracic segment by

means

of setigerous lobes, present only in the female,onthe inner surfaces of the coxopodites of thelastthree pairs of thoraciclegs.

The

fertilizedeggs are saidby Smith (1909) tobe deposited singly^"understonesand

among

the rootsofwaterplants^"

(his figureshows

them

onthebranchesof a liverwort).

The

Isopodagenerallyhave

two

separategenital exit ducts,which in the male open either by simple apertures (fig. 16A, Gprs) or through a pair of small penes on the sternum of the last thoracic segment. In the Oniscoidea, however, which include the ordinary terrestrial isopods, there is present usually a single median penis (C, D, Pen), and thegonoductsunite at its base in a

common

exit tube.

The median

penis

may

bedisplaced posteriorly so thatitarises

from

the

membrane

behind the last thoracic sternum, with its base between the appendages of the first abdominal segment (D, Pen).

The

intromittent organs of Isopoda,

when

present, are formed asin Anaspidacea of the inner arms, or endopodites, of the first and secondpairsofabdominal appendages (D, E,

Endpd). By means

of these structures masses of spermatozoa that issue

from

the gono- pores are insertedintothegenitalopeningsof the female.

The

termi- nal parts of the oviducts in

some

species of isopods are enlarged to serve as

sperm

receptacula,and the eggs are fertilized inthe ducts.

Aftermating, the female moults andinmostspeciesacquiresabrood pouch

(marsupium)

ontheundersurface of the body,intowhichthe fertilized eggs are discharged, and within which they are carried untilthe

young

hatch.

The

broodpouch is formedtypicallyby broad

NO. 14 INSECT

ABDOMEN

SNODGRASS 43 overlapping plates (oostegites) that

grow

over the thoracic venter

from

thebases of thelegs,butin

some

speciesitisformed byanterior andposterior folds of the ventral integument, and in othersby an invagination or a series of sacklike ingrowths of the

membranous

ventral wallof the thorax. Inonegenus, Paragnathia, the

young

are said todevelopintheovaries,whichserve asuteri.

The Amphipoda

areprovidedwitha pair of small penes, butthey have no organsof spermintromission;theeggs arefertilizedoutside

Gprs XnStn XmStn

Pen

Stn

Trtpd

~-Expd

"~-Endpd

E

t6.

—

Crustacea-Malacostraca-Peracarida: male genitalia of Isopoda and Amphipoda,

A, Scrolls (isopod), ventral viewof last thoracic and first abdominal seg- ments, showing gonopores on sternum of somite XII. B, Gammarus locusta (amphipod), ventral view of last thoracic segment, showing penes arising at bases of coxopodites. C, Porccllio laevls (isopod),testisand exitductofone side, and median penis. D, same, penis and first pleopods, ventral view. E, same, second pleopods.

Brn, branchia;Cxpd,coxopodite;Dct,genitalexitduct; Endpd,endopodite

;

Expd,exopodite;Gprs,gonopores;Pen, penis;Prtpd, protopodite;Stn,sternum;

T,tergum;Tcs,testis; Vsm,vesiculaseminalis;XllStn, sternumofmalegenital segment; XlllStn, sternum offirst abdominalsegment.

thebodyof the female.

The

penes, asillustrated in

Gammarus

locusta (fig.16 B,Pen),area pair of shortcylindricalprocesses arising

from membranous

areas between ^thelateral

arms

of the lastthoracic ster-

num

and the bases of the coxopodites. During mating themale at- taches himselftotheback of the femaleand remainsin thisposition until the femalemoults;then immediately the malecurves hisbody under that of the femaleand attaches small masses of spermto the bodywallof thelatter intheneighborhoodof theoviducal apertures.

The

eggs,later extruded, are fertilized in the brood pouch beneath

44 SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95 the body. It is interesting to observe that in the

Amphipoda

and Isopoda insemination of the female precedes or follows a moult by thelatteraccording as the spermatozoaare storedon orin a part of thebodynot involvedbythemoultingprocess,orina part subjectto removalatecdysis. Inseminationbefore themoultallows the develop-

ment

in the female of special ectodermal structures, such as the oostegites or brood pockets, necessary after the eggs are fertilized.

The Decapoda

vary

somewhat

in theirmatinghabits,but the sper- matozoa are enclosed in spermatophores, which either are attached totheexternalintegumentof thefemale, or are inserted intoanintegu- mental pocket {thelycum, annulusventralis) or into a pair of ecto- dermal spermathecaeassociatedwith the oviducal openings. Insemi- nation of the female, therefore, takes placeimmediatelyafter amoult toinsure againstprematurelossof thesperm.

The

external genitalia of male decapods include a pair of penes arising

from

themesalsurfaces of the coxopodites of thelastpereio- pods,andthemodified first

and

secondpleopods,whichare the active intromittentorgans.

The

genitalstructuresretain

more

of the general- ized

form

inthe

Macrura

thanintheBrachyura. In

Cambarus

virilis the penes are small

membranous

lobes projecting mesally

from

the bases of thelastpereiopods (fig. 17A, Pen), with thegonopores on their posterior surfaces.

The

sternum of thegenital segment {Stn) presentsadeepconcavitybetweenthecoxopodites,whichiscontinued forwardonthenext

two

segments,forminga ventral channel of the thorax in whicharelodged the anteriorends of thegonopods.

The

firstpair of gonopodsare long, rigid appendages (B,

D)

projecting anteriorly in the thoracicchannel as far as the bases of the second pereiopods.

The

shaft ofeachof theseappendagestaperstoaslender distal process (a), but

from

its under surface therearises mesallya large lobe thatsplitsintotwo proximal processes (D,b,c),the outer oneof which (&) has agroove

on

its uppersurface that leads intoa deep cavityat thebase of thelobe.

The

second gonopods

(E)

have

more

nearly the structure of theunmodified pleopods of the follow- ing segments.

Each

is a biramous appendage with the

two arms

{Expd,

Endpd)

supported on a two-segmented basal stalk {Cxpd, iTr).

The

larger endopodite bears a mesal lobe {d) at the end of itslongfirstsegment, which,

when

the appendageis turned forward beneaththecorrespondingfirstgonopod,claspsthe latter atthe base of its mesal lobe.

The

structure of the crayfish gonopods and the

manner

in which the appendages perform their function of sperm intromission during copulation areminutelydescribed for

Cambarus

aMnisby

Andrews

(1911).

The

spermatozoa are received from the

NO. 14 INSECT

ABDOMEN

SNODGRASS 45 penesintothegroovesof themesallobesand^thepocketsattheirbases on the firstgonopods, andare discharged into a receptacular pouch (annuhis ventralis) on the venter of the female betweenthe sterna

FiG. 17.

—

Crustacea-Malacostraca-Eucarida: male genitalia of a crayfish, Caml)a<nis virilis.

A,posteriorviewoflower partof lastthoracicsegment,showingsmall penes projecting mesally from coxopodites. B, first gonopods projecting forward, anterior (upper) surface. C, testes andvasadeferentia,dorsal view. -D,first

gonopods (normally projectingforwardinventralchannelofthorax), posterior (under)surface. E,second gonopods, posterior (under) surface.

a,distal shaft offirstgonopod; b,c,outerandinnerbranchesofventral lobe offirstgonopod;Cxpd,coxopodite;d,distallobeofsecondgonopod;Dej, ductus ejaculatorius;Endpd,endopodite;Expd,exopodite; Gpr,gonopore; Pen, penis;

PI,pleuron;Stn, sternum; T,tergum; Tes,testis; iTr,firsttrochanter (basip- odite); Vd,vasdeferens.

of the seventh and eighth thoracic segments. (See also

Andrews,

1906.)

The

crabs (Brachyura) dififer

from

most of the other decapods in that the female has a pair of large pouchlike sperm receptacles

46 SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95