NO. 6 GRASSHOPPER ABDOMEN SNODGRASS 55 The excavation of the egg cavity in the ground and the deposition

of the eggsthereinhave frequentlybeen describedin a generalway, but the process has beenclosely studied in the case of Anacridiuni aegyptium by

Fedorov

(1927),

who

confined females of this species in cages each havinga narrow, glass-walled extension of the floor, 7

mm

wide,filledwithearth.

The

diameterof the female's

abdomen

being 7

mm,

the procedure of digging and oviposition couldbe ob- servedand photographed.

The

femalegrasshopper,accordingtoFedorov'saccount,atthebe- ginningof excavation arches her

abdomen upward

anddirectsthetip of the ovipositor

downward

against the soil.

The

valves of the ovi- positor

now

beginopening andclosing,

making

a holein the earth, and the ovipositor gradually entersdeeperand deeper, while the ab-

domen

extends.

The

lengthening of the

abdomen

is accompanied by an unfoldingof the conjunctival

membranes

principallybetween ^seg- ments

IV

andV,

V

and VI, and

VI

and VII, andto alesserdegree ofthosebetween segments///and IV, and

VII

and VIII.

The

seg- ments beyond the eighth do not extend, but are even

more

closely

drawn

togetherthanusual.

The

entireextended

abdomen may

reach a length of9^{or 10}cm,its ordinary length beingabout 3^ cm.

While

digging, the part of the

abdomen

beyond the sixth segment twists through an angle of 90°,

now

to one side,

now

to the other.

The

entireprocess ofexcavating the cavityinsuitableearthwithoutspecial obstacles takes

from

i to i^ hours. ^"

The

whole complex

work

of digging,"

Fedorov

says, "

may

beanalyzedas consistingof the follow- ingsimple

movements

: (

i) putting the valves of the ovipositorto- gether, (2) a jerk

downward,

and ₍₃₎ opening the valves; apart

from

thattheovipositoristurnedby muscles

now

totheleft,

now

to theright."

Most

observers of ovipositinggrasshoppershave been

much

puzzled tounderstandthe

mechanism

of the digging apparatus, or particularly the

means

by whichthe

abdomen

is extendedto such a great length andapparently withsufficient force topenetrate the earth. Kiinckel d'Herculais (1894) noted^{that thefully}extended

abdomen

of Schisto- cerca percgrina has a length of 8 cm, while the retracted abdomen, though filledwith eggs,is only 5

cm

long.

On

^dissecting specimens with the

abdomen

protruded at

maximum

length he found the ali-

mentarycanaltocontainair;by^lettingout theairthe

abdomen

could be restoredtoitsordinarysize.

Hence

heconcludedthatthedigging insects swallow air into the alimentary tract in order to give the

abdomen

the necessary extension, the surrounding blood serving to regulate the pressure. Contrary to the opinion of most writers.

56

SMITHSONIAN MISCELLANEOUS

COLLECTIONS \0L. 94 Kiinckel d'Herculais says, themuscles play only asecondary role in the expansion of the abdomen. It has been suggested also that the

abdomen

is distended by blood pressure createdby a contraction of the thorax, butGrasse (1922) observes that thereis noexternalevi- dence of any such contraction.

A

contraction of the tergosternal abdominal muscles mightbesupposed toextend the

abdomen

length- wise, but these muscles could not in-oduce the extreme elongation

E flJ F

Fig. 23.

—

^OvipositionofAcrididae.

A,Schistoccrca percgrina, showingextent towhich the femaleabdomencan be pulled out without tearing the conjunctivalmembranes (fromVosseler, 1905).

B, C,twoattitudes ofChrysochraondispar ovipositingincutendsofraspberry stems (fromphotographs byRamme,1927). D, E,diagrams showingrelative lengthsofretractedandextendedabdomenofChrysochraondispar(fromRamme, 1927). F, grasshopper ovipositinginthe ground,showingusualposition ofab- domen (from Walton, 1916).

attained during the digging process. Grasse maintained that the ex- planation of Kiinckel d'Herculais is correct, since he

was

able to demonstratethe extension of the

abdomen

bygentlyinflatingtheali-

mentarycanal witha pipette insertedintothe

mouth

of theinsectand ligatured in the oesophagus througha hole atthe back of the head.

However,

adifferentexplanation of theabdominalextensionhasbeen proposedby Fedorov (1927)^,

who

says: "

When

the

abdomen

isfully extendeditbecomesobviousthattheexpansionisduetotheair-sacs

;

MO. 6

GRASSHOPPER ABDOMEN

SNODGRASS ₅₇ onecansee thattherhythmical

movements

of theahdomen, whichap- parentlyfacihtatethe

work

of thespiracles, result inthefillingof the sacswithair,intheirexpansionandintheexpansionof theabdomen."

Inhis

summary Fedorov

definitely states: " Inflationof theair-sacsis

the cause of the expansionof theabdomen."

Without

having

made more

than casual observationson egg-laying female grasshoppers, thewriter, after studying carefully themechan- ismof the ovipositor, has no hesitation in saying that theabove ex- planationsof theextension of the

abdomen

duringthedigging process arenotonly highlyimprobable, but are quite unnecessary. It is true thatthemusclesof the

abdomen

areentirelyinadequatetodistend the telescopic abdominal tube to the length observed, and, as

we

have seen,theprotractormusclesthatare present are limitedtothesternal region. Furthermore,the writer has frequentlyobservedthatfemales of Dissosteira Carolinatakenin late

summer

andfallhaveallthe

mus-

clesof thevisceralpart of the

abdomen

inaverylaxandapparently semidegeneratecondition,contraryto

what

isfoundinthe male. There

is no reason to doubt the observations of Kiinckel d'Herculais that thealimentary canal contains air duringthe digging process, orthat ofGrassethataninflationof thefoodtract willdistend the

abdomen

;

nor isthereanyreasontoquestion the statement of

Fedorov

thatthe air sacs

become

expanded asthe

abdomen

lengthens. It is, however, quitetoo

much

tobelievethat theobservedinflationof the alimentary canal or of the air sacscould be the

means

by which the

abdomen

is thrust out withsufificient pressure against the ovipositorto drive the latter into the ground. Insects can and do swallow air in sufficient

amount

to distend the body, as in moulting, but there is no

demon-

strated

mechanism

by whichtheycan

pump

air into theair sacs and distend these delicate vesicles against any considerable opposing pressure.

An

examinationof the

mechanism

of the grasshopper's ovipositor showsthatthelatteris an organfully competentto digits

own way

into the ground; it is a boring machine, v/hich, once set in motion with its prongs against the soil,

must

automatically bury itself, and in so doing it will stretch the easily extended

abdomen

to its full capacity, so long as the insect maintains its hold on the surface of the ground. There is thus no question of the

abdomen

forcing the ovipositor intothe earth; the ovipositor digs the hole and pulls the

abdomen

in afterit.

The

extension of the

abdomen

undoubtedlyin- volves adistention of the air sacs, and isprobably facilitated by an activeswallowingofair onthe part of the insect; in fact, ifthe ab-

domen

is actuallyincreased inbulkby^thedrawing apart of its seg-

58

SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 94 ments, it becomes amatter of necessity that there shouldbe a

com-

pensation

from some

source,and theexpansionof the air sac

would

take place automatically asinthe inspiratoryphaseof breathing.

The

observed filling of the stomach and air sacs with air, therefore, is certainly not the active cause of the elongation of the

abdomen

; it

seems

much more

probable that the inflation of these organs, fol- lowed by a closure of the

mouth

and spiracles, serves to maintain theextension of the

abdomen when

thevalvulae of the ovipositor are closed, since the latter has then no

means

of holding its position in theearth.

If

we

consider the several digging

movements

of the ovipositor con- ciselyenumerated by Fedorov,

we

can readily correlate

them

with

mus-

clesinthemotorapparatus.

The

preliminary closing of the valvulaeis effectedbythemusclesof the anterior intervalvula (fig. 17D,C,24"/,

273)^{; the}

downward

thrust must be produced by the protractors insertedontheendsof thelateral

apodemes

(C, 2^6,262);theopen- ing of the valvulaeisthe

work

of thepowerfullevatorsanddepressors (A, B, 2yi, 272) ;the twisting

movements

of the

abdomen

are ac- complished by the transverse outer dorsalmuscles between the suc- cessivetergal plates(fig. 11B,C). In additiontothesemusclesthere are the lateralretractorsof the dorsal valvulae (fig. 17 C, 26^),evi- dentlycapable of pulling the ovipositorbackintothe genitalsegments.

The

muscular equipmentof theovipositor,therefore,issuch that there isno needtoinvokeanyother

mechanism

toaccountfor theoperation of the diggingapparatusandthe stretchingof the

abdomen

than that of the ovipositor itself.

Species ofAcrididae

known

toovipositindead

wood

orinthestems of plants include ChloealtisconspcrsaHarrisof

North

America,and Chrysochraon dispar

Germ,

of Europe. Femalesof Dissosteira Caro- lina are often to be seen along railroad tracks with the end of the

abdomen

inserted into a decayed part of a tie, though, so far as thewriterknows,there isnorecord of their eggs being depositedin suchplaces.

Chloealtisconspersa is said by Scudder (1874) to select forovi- position short sticks of decaying, charred, or pithy wood, but never tochooseupright pieces of timber. ^"

The

holes,"Scudder says, "are piercedata slightangleto theperpendicular,

away from

the insect

;

they arestraightforabouta quarter ofaninch,then turn abruptlyand runhorizontally along the grain for aboutaninch.

The

eggs

(from

10 to14in

number)

arealmost alwayslaid in thehorizontalportion of thenest." Blatchley (1920) also records observationson the

wood-

excavating habits of the

same

species.

One

femalehe discovered in

NO. 6

GRASSHOPPER ABDOMEN

SNODGRASS 59