THE GENITAL CHAMBER AND THE VESTIBULUM

The

formationofexternalcavities atthebase of the ovipositor con- cealing thegonopore andthe openingof the spermatheca, and some- times theopeningof theaccessory glands,results

from

the invagination of the

body

wallatthebase of the ovipositor, usuallyaccompanied

by

a posterior extension of the eighth or of the seventh sternum.

The

sternumconcealing the cavityis

known

asthesnbgenitalplate; in

some

insectsitisthe eighth, inothers the seventh.

The

cavityheredefined as the genitalchamber,or bursa copulatrix (fig. 8B,

GC)

isthat

formed

by an invagination of the part of the

body

wallabove theend of the eighth sternuminwhichare situated theopeningsof themedianoviductandthe spermatheca.

The

ventral wall of thegenital

chamber may

contain the reflected posterior part of the eighth sternum.

The

oviductus

communis (Ode)

openseither

on

the floor of the genital

chamber

or into its anterior end.

The

spermatheca (Spt) openstypically inthe dorsal wall of thechamber, morphologically posteriortothegonopore.

The

actualrelation ofthe

two

openingstoeachother,however,varieson accountof the variable position of thegonopore, thelatter,

when

^locatedon^thefloorof the

36

genital chamber,beingbelow and oftenbehindthepointatwhichthe spermatheca opensintothe dorsal wall of the chamber.

In

some

insectsthe spermatheca appearsto arise

from

the dorsal wall of themedian oviduct, but itis probable thatin all such cases the part of the median egg passage receiving the spermathecal duct

is formedasan extension of thegenital chamber. There canbeno doubt, forexample,that the copulatorypouchof thecicada (fig. 32,

GC)

or of thehoney bee (fig.44^{B, b), into}which thespermatheca opens, is apart of the genital chamber, anditseems equally certain that theso-called "uterus^"of viviparousDipteraislikewiseaspecial compartmentof thegenital chamber. Sinceinmostcases the^genital

chamber

receives the male organ during mating, it is functionally a

"bursa copulatrix^".

When

thegenital chamber, orananterior part ofit,however,takes the

form

ofa tubularpassageleadingback

from

the true oviduct,^itshouldbecalledthevagina, asby

Demandt

(1912, Korschelt,1924) ⁱⁿDytiscus,and by

Imms

(1930),

Heberdey

(1931), andothers, todisilnguishit

from

the trueoviductus

communis

(Eier- gang).

Much

confusionexists in descriptiveworksas tothedistinc- tionbetween medianoviductandgenital chamber,or vagina.

A

safe rule to follow is that the oviduct lies anterior to the

mouth

of the spermatheca, and the genital

chamber

(vagina, or "uterus") pos- teriorto it.

Morphologically the terminus of the oviductus

communis

in the genitalchamber,or vagina, should be distinguished

from

the posterior opening of thelatter to theexterior.

The

opening of theoviduct is

the truemedian gonopore, whether exposedexternally,orconcealedin the genital

chamber

;

when

the genital

chamber

is converted into a copulatorypouch or a vaginal tubewithanarrowedexit,itsposterior opening, whether onthe eighth or the ninth segment, is the ostium vaginae, or vulva.

When

theseventhsternumis extendedbeyondtheeighth sternum

(fig.

8

C),thelatter (VlllStn) isgenerallyreducedinsize,and

may become

rudimentary,oritisretainedonly as a smallplateonthefloor of thegenital

chamber

containing the gonopore. Thisconditionischar- acteristic of Termitidae, Blattidae, Hemiptera, and Hymenoptera.

The

extension of theseventhabdominal sternumbeyondthe eighth produces a second cavity (fig. 8C, Vst) lying above the seventh sternum, which becomes an antechamber to the primary genital

chamber (GC),

or a continuation of the latter, and

may

bedistin- guishedas thevestibulum.

With

insectsthat retain a generalized structure inthegenital seg- ments, the base of the ovipositor usuallylies in thegenital chamber.

NO. 8 INSECT

ABDOMEN

SNODGRASS 37 and the eggs discharged

from

the gonopore located on the floorof the

chamber

arepassedintothe channel of the ovipositorbetweenthe bases of thefirstvalvulae. Thisconditioniswellillustrated inAcridi- dae, Tettigoniidae,and Gryllidae. Since thefirstvalvifers, however.

are always distinct

from

the eighth sternum, they

may

be displaced posteriorlytosuchanextentthatthe ovipositor baseliesentirelypos- terior tothe genital chamber. Thiscondition is found especially in insects in whichthe seventh sternumis prolonged, for insuch cases the eighth sternumis generallyreduced (fig.8C, VlllStn) andthe genital

chamber {GC)

becomesa

mere

pocket of the anterior wall of the vestibulum {Vsi).

An

unusual condition, to be described in detaillater, occurs in

some

of the Cicadidae,inwhich the highly de- velopedgenital

chamber

hasa secondposterior opening on the ninth venter (fig.

8D).

THE

OVIPOSITOR

An

ovipositorformed

from

appendicular processes of the

abdomen

isingeneral present onlyin insectshavingthefemalegenital opening on the eighth abdominal venter, or between the eighth and ninth sterna.

With

the transposition of the genital opening to the ninth segment, the ovipositor has been suppressed inall cases (except in Cicadidaehaving

two

genitalopenings,inwhichthetgg passageleads directly into the channel of the ovipositor; and it should be noted also thatthefemaleexitapparatusof the

Homoptera

ingeneralisnot well understood). Apparent rudiments of thegonopods of the ninth segment,however,

may

beretained,asinPanorpidae

and

Coleoptera.

A

comparative study of the plates and appendicular structures as- sociatedwiththefemalegenitalopeninginColeoptera hasbeen

made by Tanner

(1927),

who

claims that the terminal hooksor spurs are styli;but the general structureand musculatureof theorgansdoes not correspond closelywith that of the parts of a typical ovipositor be- longing to the ninth segment.

The

^{principal groups}of pterygote in- sects in which an ovipositor is well developed are the Orthoptera, Hemiptera, Thysanoptera, and Hymenoptera. In various other orders, however, an ovipositor

may

be present in

some

members, eitheras afully developed organor inarudimentary form.

The

fundamental structure of the ovipositorisalwaysthe same,andthewideoccurrence oftheorgansuggeststhatanovipositor

formed

of theappendagesof the eighth

and

ninth abdominal segments

was

a character of the

common

ancestors of the

Thysanura

andPterygota.

The

pterygote ovipositor, in its typical form, consists of a shaft

and

a basalmechanism, andusually includes a pair of accessorylobes.

38 89

The

shaft is

composed

generally of twopairs of bladelike processes, thefirstand secondvalvidae (fig. 9,iVl,2VI).

The

^basal

mechanism

consistsessentiallyof four lobes orplates,thefirstand secondvalvifers {iVlf, 2Vlf), associatedwith the eighthand ninth segments of the abdomen,togetherwiththeirconnectedmuscles.

The

accessorylobes, or third valvidae (3VI),areborneatthe posteriorendsof thesecond valvifers. In

some

insectsthe basal structure of the ovipositor includes medianscleriteslyingbetweenthesecondvalvifers,

known

astheinter- valvulae, and also muscles inserted onthese sclerites.

The

firstand

\

\

Ode ^iVlf vinstn 2Vir

Fig. 9.

—

^{Diagramof the basicstructureof thepterygote} ovipositor.

Each gonopodconsists ofa basalplate,or^valvifer (iVlf,2VIJ),anda gona- pophysis,or valvula {iVl,

2V

I); each valvifer provided with muscles arising onthetergumofits segment; the basis ofsecondgonopod produced^{distally in} a free lobe, the third valvula {3VI); gonopore {Gpr) at base of ovipositor aboveeighthsternum.

secondvalvulaearise

from

the anteriorends of thefirstand second valvifers,respectively.

The

third valvulae, arising

from

the posterior endsof thesecond valvifers,are usually freelobes, butin most

Or-

thopterathey

form

a third pair of bladesinthe shaftof theovipositor.

The

^{first valvifers} in the Hemiptera are closely associated with the lowermarginsof the eighth tergum,thoughthey are unitedby mesal extensions with the ninth tergum; in Orthoptera and

Hymenoptera

they

become more

or less displaced posteriorly, andarticulated with theninthtergum, orwiththesecondvalvifers.

The

secondvalvifers arealways associatedwith the ninth tergum.

The

dorsalmuscles of thefirstvalvifers,regardless of the position oftheplatesthemselves.

INSECT

ABDOMEN

SNODGRASS 39 invariably taketheiroriginontheeighthtergum (fig.9) ^;the dorsal muscles of the secondvalvifers arise onthe ninth tergum.

From

thissketch of the

more

generalized structure of the ovipositor inpterygoteinsectsitisclearthattheorgan

may

be derivedtheoreti- cally

from

a pair ofgenitalappendages havingthe

same

structureand the

same

relations tothe eighth and ninthsegments of the

abdomen

ashavethe female gonopods in theThysanura.

Thus we may

con- ceive that the parts of the pterygote ovipositor belonging to the eighth segment ^(fig. 10

A)

^{represent the limb bases}

(LB)

of a pair of gonopods, which

become

the first valvifers (B, iVlf), and a pair of corresponding gonapophyses (A, Gon), which

become

the firstvalvulae (B, iVl).

The

^{styli of thefirst}gonopods (A, Sty) are

GprLB(iVlf)

3

Fig. 10.—Analyticaldiagramsofthemorphology ofthe pterygoteovipositor.

A, ventral view of theoretical generalized structureof eighth segment and gonopods (cf.fig.6 E,fig. 7A).

B,lateralviev^rofgeneralized eighthsegmentandfirstgonopod;stylusabsent inallpterygoteinsects.

C, lateral viewof generalized ninth segment and second gonopod; basis of gonopod {LB) subdividedintosecondvalvifer {2VIJ) andthird valvula {3VI), stylus {Sty)sometimespresent.

absentinallpterygoteinsects (B).

The

gonopore (A, Gpr)islocated typicallybehindorabovethe posteriormarginof the primitivesternum of the eighthsegment {Stn), but between the proximal endsof the limbbases. It is,then,buta secondary matterifthe limb baseplates, or valvifers, of the eighth segment

become more

or less dissociated

from

the eighthsegment (B)

and

variously connectedwith the ninth tergumorwiththesecond valvifers.

As

abovenoted, thefirstvalvi- fers,regardless oftheirdisplacement, retaintheirmuscleconnections with the eighth segment.

The

parts of the pterygote ovipositor be- longing to the ninth segment

may

be supposed in the

same way

to representcorrespondingparts ofthesecond gonopods of Thysanura, thesecondvalvifers (fig.10 C,sVlf) being limbbases,andthesecond valvulae {2VI) the second gonapophyses.

40

89

The

terminal lobes of the second valvifers (figs. 9, 10 C, jVl) might suggest bytheir usual position that they are the styli of the second gonopods;but, as will be

shown

presently, itis certain that they aresecondary outgrowths of the

gonopod

bases.

They

arehere termed ^"third valvulae " because in the Orthoptera they resemble thefirst and secondvalvulae, and

form

a third pair of bladesin the shaft of theovipositor. Usuallythe third valvulae ensheath thedistal part of the ovipositorbetween their concave inner surfaces.

The

sclerites termedintervalvulae, lying betweenthe bases of the secondvalvifers,evidentlybelongto the venter of the ninth segment, and probablyrepresent scleroticremnants of the ninth sternum.

A

review of the history of opinionconcerningthemorphology of theinsect ovipositor

would

occupy

more

space than its value

would

justify.

The

theory here elaborated isessentially that

now

current withstudents ofinsectanatomy,.except thatithas notbeengenerally recognized that the firstvalvifersare the bases of thefirstgonopods.

Some

writershaveclaimed that theseplatesbearing thefirstvalvulae are derived

from

theeighth sternum,andothers thatthey are a part of the ninthtergum.

The

difi^erenceofopinionhas arisenprobably

from

thefactthatthe position of the^firstvalvifersrelative tothesurround- ing parts differs considerably in different insects according to the

mechanism

of theovipositor. In

some

insectstheplates clearlybelong anatomicallytothe eighthsegment, sincetheylieinthe pleural areas of thissegment between thetergum andthesternum^;inothers they are dissociated

from

the eighthsegmentandarehingedtothesecond valvifers;instillothersthey aredefinitelyarticulatedwith,or attached to, the ninth tergum. If, therefore, the ^firstvalvifers appear tobe derivedintheirdevelopment

from

the eighth sternum, the ontogenetic facts

mean

simply thatatanearly stage the bases of thefirstgonopods arenot distinguishable

from

the truesternalarea ofthissegment;on theother hand,ifthefirstvalvifersappeartobe cutoff

from

the ninth tergum, it is probable thattheirphylogenetic historyis not fully re- capitulatedin theirontogeneticdevelopment.

The

invariable origin of the musclesof the plates inquestion ontheeighth tergumleaves no doubt that theplates belongtotheeighth segment,andthe fact that theplatesalwayscarry thefirstvalvulaewould seemtobeproofthat they are the bases of thefirstgonopods.

The

term^"valvifer^"

was

firstintroducedintothenomenclatureof the ovipositorby

Crampton

(1917)todesignate thescleriteherecalled

"_first valvifer^" supporting the first, or ventral, valvula, and is so usedby

Walker

(1919).

A

smallplate atthebase of thefirstvalvula

Crampton

called the " basivalvula^". In a later paper containing a

NO. 8 INSECT

ABDOMEN

SNODGRASS 4I

more

extensivecomparativestudy of theovipositor,however,

Cramp-

ton (1929) ^repeatedly confused the valvifer and the basivalvulabe- causehe did not base his identifications of these sclerites on their relations totherest of the

mechanism

of the ovipositor. His^*'val- vifer" in Gryllohlatta, Centhophilus, Gryllus,and Hymenoptera, ^for example, isthescleritehecalls" basivalvula" inHemiptera, whilein Periplaneia hegives the

name

^"valvifer " to a sclerite that belongs tothe ninthtergum.

The

scleritedesignatedfirstvalviferinthe present paper, therefore, is the ^"valvifer^" of

Crampton

as he applied the term in Grylloblattidae, Tettigoniidae, Gryllidae, and Hymenoptera, and the homologous sclerite in other insects as determined

by

its

muscle attachments

and

its relationtothefirstvalvula. Inhishypo- theticaldiagrams

Crampton

_(1929,figs.1-4) derives the valvifer

from

theninthtergum, probably becausethescleritehecalls "valvifer "in Blattidae isa part of the ninthtergum,buthegives^itnoconnection withthefirstvalvula,thoughthisisitsmost distinguishingandchar- acteristicfeatureinthe

mechanism

of the adult ovipositorinallinsects.

Crampton's diagrams, however, do not represent actual anatomical conditions,anditisonly

by

a detailed dissection of the partsinques- tion thatthe trueidentities oftheA^ariousbasal elements of the ovi- positorcanbe determined.

Since thetermvalvifer^isa veryappropriateone

when

consistently used, inasmuchasitsignifies literallya scleritesupportingavalvula, thewriterhere introduces the innovation ofextendingittobothpairs of valvula-bearing plates, distinguishing those that carry the first valvulae as thefirstvalvifers,

and

thosethatcarry thesecondandthird valvulae as thesecondvalvifers (usuallycalled" coxites^"of theninth segment).

The

term basivalvulafittingly signifiesthe small sclerites that sometimesoccuratthe bases of the firstvalvulae, so

named

by

Crampton

(1917, 1929) ⁱⁿGryllohlatta, Tettigoniidae,

and

Gryllidae.

The

leadingfacts intheontogeneticdevelopment of the ovipositor are too well

known

to be given here

more

than a brief review. All investigatorsagreethata pair of processes

grow

out

from

theunder surface of the eighthabdominal segment, andasecondpair

from

the undersurface of the ninthsegment,

and

thateach of the processes of thesecondpairtypicallybecomes double bydividing lengthwise, orby budding an inner lobe

from

its mesal surface.

The

processes of the eighth segment in most cases

become

the first valvulae; the outer processes of theninth segment

form

the secondvalvifers, including the terminal lobes of thelatter,while the inner processes

become

the secondvalvulae. It isclaimedby Nel (1930) ^{thatthedefinitivefirst} valvulae of

Odonata

and Orthopteraare not thegonapophysesof the