52 SMITHSONIAN MISCELLANEOUS COLLECTIONS

tettigoniidtype.

Walker

says that ^{" in}the external

form

ofthe val- vulae andtheir connectionswith neighboringsclerites Grylloblatta is

remarkablylike a primitive Tettigoniid,such as CeufhophHus."

The

three pairsof valvulae are well developed, but the dorsaland ventral pairsarenot connected,andthemedianpairisexposed between them.

The

basivalvulae

form

distinct scleritesbetweenthebases of the ven- tralvalvulaeandthe eighth sternum.

Crampton

believes thatthebasi- valvulae are derived

from

the^"coxites " of the eighthsegmentof the

nymph,

buthe givesno evidence that thesclerites inthe

nymph

are limb base elements.

The

presence of well-developedstyliontheends of the dorsal valvulae in the

nymph

of Grylloblatta, which are lost in the adult, is a primitive feature retained likewise in the

young

ofBlattidae.

GRYLLUS

ASSIMILIS FABRICIUS

Since thecricket isagoodsubject for school laboratorywork,itis here selected for a detailed study of the orthopteroid

abdomen

and ovipositor.

The abdomen

of the cricket gives a fairly generalized example of the typicalstructure of theabdominal part of theinsect body.

The

ovipositor, however, is by no

means

generalized; it is specializedinthe

way

the ovipositor of all Orthoptera is specialized, and in addition it is one of the most highly perfected egg-laying mechanisms found

among

the insects.

The

visceralregion of the abdomen.

— The

pregenital segments of thecricket's

abdomen

areall welldevelopedinboth themale andthe female (fig.14

A),

andcontaindistincttergalandsternal plates.

The

terga (T)areseparated

from

the sterna(Stn) byawide

membranous

or coriaceous areaoneachside of the body, containing the spiracles.

Running

lengthwisethrougheach of these

membranous

areas, below thespiracles, is aprominent lateral fold (a-a).

The

^relationsof the parts of the

abdomen

above and belowthelateral fold to each other andtothecorrespondingparts ofthethoraxattestthatthe fold

marks

the site of the dorso-pleural ^line.

The membranous

area above the fold, containing the spiracles, is, therefore, the laterodorsal region, or paratergal area of the

dorsum

(Id),andthatbelowthe foldisthe true pleural area (P). Anteriorlyitisseen that thelineofthedorso- pleural fold on the

abdomen

extends into the thorax dorsal to the thoracic pleural plates,or subcoxae (Sex),

and

that the pleural area continued

from

the

abdomen

here expands betweenthemetathoracic tergum and sternum (T3,StUs) toinclude the thoracic pleura, or sub- coxal parts of thelegbases. Posteriorly thelineof the dorso-pleural fold extends, inthe female (B, a),between thetergumof theninth

NO. 8 INSECT

ABDOMEN

SNODGRASS 53 segment

(IX)

andthe basal plates of the ovipositor (Ovp). This relationis

more

clearly

shown

ifthe

dorsum

ofthe

abdomen

issepa- rated

from

the pleurosternal parts (C), the dorso-pleuralline (a-a) being theoretically carried out above the bases of the cerci (Cer).

It isthustobe seen that the basalplates of theovipositor (C, iVlf, 2Vlf) belong^tothe pleural area of the

abdomen

(P), andthat,there-

Sex

Abdomen of Gryllusassimilis.

A, lateral view of male abdomen and metathorax, showing groove (a-a) along dorso-pleural line above thoracic subcoxae and limb base, or pleural, region(P)ofabdomen.

B,endofabdomenoffemale,showingrelation of baseofovipositortoeighth andninthsegments.

C,samepartofabdomenseparatedalong dorso-pleural line (a-a).

fore,theycorrespondinposition, atleast,withthe subcoxalplates of the thoracic legbases (A,Sc.v).

A

^closer study of the

membranous

lateral areas of the visceral region of the

abdomen

(fig. 15

A)

showsthatthe dorso-pleural fold (a-a)oneachsideisborderedaboveby an undulatingseriesof slender sclerotizations, and below by a similar series of

somewhat

thicker sclerotizations.

The

upper seriesevidently

marks

the lower edge of the

dorsum

(D), andthe lowerseriestheupper edge ofthe pleuro-

54 89 ventral region

(PV). The

sclerotic thickenings

form

attachment points formuscles

on

the innerabdominal wall (B).

The

musculatureof thevisceralsegmentsinthe

abdomen

ofGryllus comprisestheusualdorsal, ventral, lateral,transverse,

and

spiracular muscles.

The

followingmuscles

may

be distinguishedinanindividual segment, suchasthefifthor sixth,

shown

at

B

of Figure15.

The

dorsalmusclesconsist of

two

setsof longitudinalfibers,both of which apparentlybelongto the internal system, since no muscles

\

NO. 8 INSECT

ABDOMEN

SNODGRASS ₅₅ trals (ve) lyingbeneaththeothers, wheretheyarisenear themiddle of each sternal plate and are inserted posteriorly on the anterior marginof the sternumfollowing.

The

transverse ventrals consist of wide bandsoffibers (tv) crossing the anterior parts of thesegments internal tothe longitudinalventrals,andattachedlaterallyontheedges of thesternal plates.

The

lasttransverse ventralinthefemaleisthat of the seventhsegment ^(fig. 19 A, tv).

The

lateral muscles include tergosternal, tergopleural, paratergo- sternal, and pleurosternalmuscles. Ineach segment there is a large tergosternallateralmuscle (7) arisingonthe posteriorlateralpart of thetergumexternaltothelateral dorsals,andinsertedonthe posterior lateralmarginof the sternum. Justbehind thismuscle, andexternal to it, are

two

tergopleural muscles _{(2, 3)} takingtheir origin onthe lower edgeof the tergum.

The

first (^) ^is attached ventrallyonthe pleuralmarginof the

same

segment;thesecond _(j) isintersegmental since itis attached on the pleural margin of the following segment.

The

paratergosternal muscles comprise

two

bands of fibers (4, 5) on the middle of each segment, one before, the other behind the spiracle dilator (dis).

The

pleurosternal muscles include likewise

two

bandsof fibers,one (d) inthe anterior part of each segment, the other (7) ⁱⁿthe posteriorpart.

The

spiracularmusclesare theusual antagonistic pair insertedon the

manubrium

of the anteriormovablewall of the spiracular atrium.

One

isaverysmall occlusor arising onthe posterioratrial wall;the other is a large dilator (dls) arising ventrally on the edge of the sternum between^theattachments of ₄and5.

The

somatic muscles of the visceral region of the cricket's ab-

domen

are used by the female principally for respiratory purposes, since oviposition is accomplished by the muscles of the genital seg- ments, and ordinarily involves

few movements

in the rest of the abdomen.

The

mechanicalrelationof thelateralmusclestotheskeletal parts of the

abdomen

is

shown

diagrammaticallyat

A

of figure 16.

It is to be noted that the muscles can produce only a contraction of the abdomen, brought about mostly by a lifting of the sternal plates, since there is no antagonistic

mechanism

capable of dilating the abdomen, either dorso-ventrally or longitudinally, such as that developed in the Acrididae. Inspiration with the cricket, therefore, mustbeaccomplished bya passiveexpansion ofthe abdominalparts compressedby muscularforce.

The

genital segments and the ovipositor.

— The

genital segments of the female cricket (fig. 14 B, VIIT,

IX)

are

somewhat

reduced by comparison withtheeighth andninthabdominal segments of the

S

56

SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 89 male (A).

The

shortened eighth tergum (B, VIII) ends belowina point separated by the dorso-pleural fold

from

the small eighth sternum (VlllStn), whichprojectsbeneaththebase of the ovipositor as a small subgenitalplate.

The

ninthtergum

(IX)

isnarrowedabove, butiswidened onthesides,and extends

downward

tothebase of the ovipositor.

The

venter of the ninthsegmentisnotvisibleexternally

it is the narrow,

membranous

ventral wall of the segment between the basal halves of theovipositor,containing anteriorlyandposteriorly

]5t dim

J.

PlStn

V

^{i_Stn_ ^<}

^^ ^ ^C

VNC

. ve vi

A C

^PlStn.

Fig. 16.

—

^Abdominal structures of GryllusandBlatta.

A, diagrammatic cross-section through abdomenof Gryllusassimilis, show- ingrelation ofintegumental areasandmusclesillustrated inFigure15.

B, lateral parts of abdominal segment of Blatta orientalis with dorsal and ventralplatesseparatedtoexpose the dorso-pleuralfold (a-a).

C,diagrammaticcross section ofabdomenof Blatta,showinginfoldeddorso- pleural membrane (a),and position oflateral muscles (li).

the sclerotic intervalvular bridges (figs. 17

H,

18, aiv, piv). In the maletheninthsternumisfullyexposed,and formsa large subgenital plate (fig. 14A, IXStn).

The

innersurfaces of the eighthandninth terga of thefemale (fig.18) are enlargedbythinapodemalextensions

from

their anterior margins, giving attachment to muscles of the ovipositor.

The

ninthtergumhas a stronglydevelopedantecosa (Ac), whichterminatesina ventral process bearing a socket (a) forarticu- lationwith the basal part of theovipositor.

The

musculature of thegenital segments ismostly adaptedto the

mechanism

of the ovipositor.

The

dorsal muscles,however,

conform

withthose of thevisceral segments,andin the eighthsegmentthere areoneor

two

pairs of

weak

lateral musclesinserted below nearthe margins of the eighth sternum.

The

other lateral muscles in both genital segments are highly developedas muscles of the ovipositor (fig. 17E). Ventral muscles are absent inthe eighth segment, and those of the ninthsegmentare of doubtful

homology

with the ventral musclesof thevisceralsegments.

NO. O INSECT

ABDOMEN

SNODGRASS 57

The

ovipositor of thecricketconsistsof a small basalpart,attached to the ninth abdominal segment (fig. 14B),

and

of a long, slender shaft terminating in a sharp-pointed enlargement (fig. 17B).

The

shaftisformedof the^firstandthirdvalvulae (figs.17 A, E, 18,iVl, 3VI), which are respectively ventral and dorsal in position relative to eachother.

The

second valvulae are reduced to a pair of small,

membranous

lobes (figs. 17 E, G, 18, 2VI) arising

from

the venter of the ninth segment between thebases of the dorsal valvulae.

The

base of the ovipositor consists of thefirstand secondvalvifers (figs.

14 C, 17A,iVlf,2Vlf), andthe anteriorandposterior intervalvulae (fig.

17H,

aiv, piv).

The two

valvifers on eachside are closely as- sociatedwiththelovv-eredgeof the ninthtergum,buttheirtrue seg- mentalrelationsare

shown

bythe origins oftheirdorsalmuscles (fig.

17E), those of thefirst valvifer (j) arising onthe eighth tergum, those of thesecondvalvifer _{6, 7) onthe ninthtergum.

The

connec- tionof thefirstvalviferswiththeninthtergumisevidently asecondary association,since itisclearlyan adaptation to the special

mechanism

of the orthopteroidtype ofovipositor.

The

first valviferis an irregularly triangular plate (fig. 17A, F, iVlf). Itsonlyconnection withtheeighthsegmentis

by

the pleural

membrane

uniting the eighth tergum and sternum; otherwise its associationsareentirely withthe ninth segment, except forits

mus-

culature.

By

a strongly developed condyle near the middle of its dorsal margin (F, a), the first valvifer freely articulates with the lower extremity ofthe antecosta {Ac) of theninth tergum. Itsan- teriorendis producedintoa tapering process {e) for theattachment of muscles.

At

itsposterior angle ithas a narrow, flexibleexternal connection with the second valvifer {A, b), internal to which is a deep notch (F, d)

by

whichthefirstvalviferarticulateswitha con- dylarsurface (G, h) of thesecondvalvifer(figs. 17

H,

21,dh).

Ven-

trallythefirstvalviferiscontinuousbyanarrow,flexibletongue (fig.

17A,F, c) withthefirst,orventral,valvula {iVl).

From

the inner face of thefirstvalvifer, abovethe innerarticulationwiththesecond valvifer, there arises a large flat

apodeme

(F,

H,

/), giving attach-

ment

toathick, cylindricalmuscle (E,

H,

p)

from

amedian

apodeme

{k) of the posterior intervalvula (piv).

The

second valvifer (fig. 17A, G, 2Vlf) is of a

more

irregular shape thanthe first,

and

its ventral part is directly continuous into thethird, ordorsal,valvula (3VI). Itsposteriorend, justbefore the base of the valvula, isproduced

upward

inabroad dorsal

arm

(G,i),

which terminates in an apodeme, the superior apophysis, projecting within the ninthtergum (A,i).

The

anterior extremity of thesecond

m

^3VI

iW

^{aiv 2Vir 10 iVl}

Fig. 17.

—

^{Details of structure and} musculature of ovipositor of Gryllus assimilis.

A, baseof ovipositor, showingarticulation of firstvalvifer (iVlf) atawith ninthtergum,andathwith secondvalvifer.

B,C,D, apicalstructureof shaft ovipositor.

E, innerviewof genitalandtenth segments, withright half ofbaseof oviposi- torandmusclesofsameside.

F, innerviewofright firstvalvifer, showing its articulation (a) with ninth tergum,itsanteriormuscles,andconnection (c)withfirstvalvula.

G, inner view ofright second valviferandits muscles _(6,7), togetherwith anterior intervalvula {aiz'), rudimentary second valvula {2VI), and base of thirdvalvula (sl'l).

H,dorsalviewofvalvifersandintervalvulae,and^theirmuscles;firstvalvifers (iVlf) articulateddorsally (a) toninth tergum (/AT), posteriorly (dh) to secondvalvifers {^I'lf);secondvalvifersconnected anteriorly by anteriorinter- valvula (aiv) and posteriorlyby posterior intervalvula (piv).

58

NO. O INSECT

ABDOMEN

SNODGRASS 59 valviferformsasecondstrong process, the inferiorapophysis (G,

H,

g).

The

articular condylebywhichthesecond valvifer ishingedto the first is located on the inner face of the anterior margin of the dorsal

arm

(G, h).

The

secondvalvifer of thecrickethasnodirect connection with the ninthtergum.

Two

intervalvularscleritesare welldevelopedinGryllus.

The

first, or anterior intervalvula (fig. 17

H,

aiv), isa transverse bar between the anterior processes (g) of the secondvalvifers. Mediallyitbears asmall

apodeme

(;').

The

second, or posterior intervalvula (piv), is a broad, externally convex plate exposed above the bases of the dorsal valvulae (A, piv).

By

its produced lateral extremities it articulates with the second valvifers at the deeply notched angles betweenthe dorsal

arms

of thelatterandthebases of the dorsalval- vulae

(H).

Mediallythe posterior intervalvula bears a high, plate- like

apodeme

(E,

H,

^). In a lengthwise section of the

abdomen

(figs. 17 E, 18) ^itisclearlyseenthatthetwointervalvulae {aiv,piv) belongto the venter of the ninth abdominal segment, andthat they havethestatusof anteriorandposteriorsternal scleriteslyingbetween thesecondvalvifers. Tergal musclesof theninthsegmentare inserted on each of theintervalvulae.

The

reduced eighth sternum, which forms a free subgenital plate (fig. 18, VlllStn) beneaththebase of theovipositor,conceals a small genital

chamber {GC)

^{above its} dorsal wall, between the bases of the valvulae. Into the anterior end of thegenital

chamber

the short median oviduct

(Ode)

opens between

two membranous

folds (fig.

19 B,/) on^thedorsal surface of the subgenitalplate. Dorsalto the openingof the oviduct, the anterior dorsal wall of thegenital

chamber

before the anterior intervalvula {aiv) forms adeep pouch (t) pro- jectingintothebodycavityabovethe oviduct.

The

pouchcontainsa stronglysclerotized, spoutlikeorgan (u) reflected

from

its anterior wall, which is transversed bythe terminal part of the spermathecal duct (SptD).

The

^deflecteddistalextremityof the spout,containing the opening of the sperm duct, projects into the genital

chamber

a little beyond the opening of the oviduct.

The

eggs issuing

from

the gonopore arethus, evidently, fertilized just before entering the channel of the ovipositorbetweenthebases of the valvulae.

The

shaft of the ovipositorconsistsof theslender,elongatefirstand third valvulae.

The two

valvulae on each side are firmlybut freely interlockedbya ridgewithanexpanded margin ontheloweredgeof the dorsal thirdvalvula (fig. 20) that isheld in agrooveonthe ap- posed surface of the ventral first valvula.

The

valvulae of opposite sides are not united.

The

inner walls of the dorsal valvulae are

6o

SMITHSONIAN MISCELLANEOUS

Strongly sclerotized throughout, and each is strengthened by a high internal ridge.

The

ventral valvulae are

membranous

and flexibleon theirmesalsurfaces,andthe inner wall of eachisthrowninto alongi- tudinal fold.

The

muscles of the ovipositor.—

The

musculature of the cricket's ovipositor is strongly developed, but isnot particularlycomplex. It includes the ventral muscles of the seventh abdominal segment, and the principal lateralandventral musclesof the eighthandninth seg-