COLLEMBOLA

NO. 14 INSECT

ABDOMEN —

^SNODGRASS 65 Phallus (Pill).

— ^The

^{usual median penis or single} intromittent organofmaleinsects,variously formed and probably developedinde- pendentlyinseveral insectgroups.

Preputialsac.

—

^Seeendophallus.

Siibgenitalplate

(IXS). —

See hypandrium.

Titillators (Ttl).

—

^Distalexternalprocesses of theaedeagus.

Virga (Vir).

— A

terminal phallicspine or slenderrod usuallyaris- ing

from

the wall of the endophallus and therefore protractile with the aversion of thelatter.

66

SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95 lateralwall of the gonadialsac (B,D, G, Grin), and in this feature the gonads of certain Collembola preserve the generalized structure of the reproductiveorgans foundinOnychophora, andinarthropods

Fig.23.

—

Hexapoda-Collembola^: internalgenitalia.

A,Amiridamarithna,diagramofposition ofmalegonads (from Imms, 1906).

B, Amirophoriis lands,outline of testes showing position of germaria (from Lecaillon, 1902a). C,Amiridamaritima, transversesection throughfourth ab- dominal segment (from Imms, 1906). D,Amirophoruslaricis,transverse sec- tion oftestis, showinggermarium in dorsal wall (from Lecaillon, 1902a). E, Anurida maritima, longitudinal ^section of posterior part of testis, showing bundlesofspermatozoaseparated by ingrowthsof epithelialwall (from Imms, 1906). F, Podura aquatica,mature testis, dorsal view (from Willem, 1900).

G, Tomocerusvulgaris,maturetestisof rightside,dorsal view (from Willem, 1900)

.

a,intratesticularingrowthsoftesticularepithelium;BMb,basementmembrane;

Dej, ductus ejaculatorius; DMcl,dorsal longitudinalmuscles;

DV,

dorsalblood vessel;Epth,testicularepithelium; Ft, fat tissue; G,gonad, G>rm,germarium

;

Sp::, spermatozoa; Tes, testis; Vent, ventriculus;

VNC,

ventral nerve cord

;

Vsm,vesiculaseminalis.

Other thaninsects inwhich thegerminalcellshavenot

become

local- izedintheapex of thegonadsor inthe apices of lateral diverticula.

Withinthe

lumen

of thetestisthebundles of developingspermatozoa (E, Sps) are enclosed in compartments formed of intratesticular

J

NO. 14 INSECT

ABDOMEN

SNODGRASS 67 prolongations (a)

from

the epithelial walls (Epth) of the gonad.

The

testicular cysts of other insectsare said to be formed of cells

descended

from

the spermatogonia.

The

simple shapeof the gonadsis most fully carriedoverintothe adult stageinAnurida, in whichthe ovariesandtestes, thoughthey

may

increase greatlyin size fromtheimmature stages, retain for the most part an undivided saclike

form

(fig. 23 A, B).

The

germinal area of Anurida, as described by Lecaillon (1902) and by

Imms

(1906),^{lies in}the dorsalwall of thegonad (D,

Grm).

Inthe male,

Imms

says, "the germinaltissue is in the

form

of a massorridge, situated atabout themiddleof the length of the testis^",inthe female

it formsineach ovary^"aprotrudingridge lyinginthe region of the third and fourth abdominal segments." In Podura, according to

Willem

(1900), the adultgonads are voluminous organs occupying the

abdomen

andthelasttwo segmentsof the thorax.

Each

gonadis an irregular sac (F) with its mesal wall produced into five large pouches separated by deep incisions, but the germarial zone of the testis extends through the entire length of the dorsal wall of the organ, both on theundivided lateral partand on the mesal pouches.

In theEntomobryidae.as

shown

by

Willem

(1900), ^theimmature gonadsare simplefusiformsacsasinthe

young

of Poduridae,butin each sex the

germarium

is localized in the apex of the organ, evi- dentlyasecondarycondition,

Willem

contends.

As

developmentpro- ceeds, however,eachgonad growsanteriorly andposteriorlybeyond thegerminal zoneineachdirection,withtheresult that inthedefini- tive organ, the

germarium

is a restricted area of the lateral wall of the gonad near the posteriorend of the latter (fig. 23 G,

Grm).

In this family thegonad becomes two-branched by^thedevelopmentof a longmesallobe opposite thegermarium.

The

gonadsof Neelidaeand Sminthuridae are undivided tubes, but eachtubeis bent

upon

itself because of the limited space inthe globular abdomen. According to Lecaillon (1902) the germinal zonein the maleof these families is restricted to the apex of the testis; in the female of Sminthurns,

Willem

says, the germinal region of the ovary lies ventrally in the outer wall of themiddlepartof thetube,but

much

nearer the anterior endof thelatterthaninPoduridae and Entomobryidae.

From

the above review of the structure and development of the coUembolan gonads ^it is evident that the organs, beginning with a generalized condition,have followed a line of specialization confined totheCollembola.

The

primitive gonadial sac.as representedbythe testisofPoduridae, probably hada germarialbandinits dorsalwall.

The

localizationof the

germarium

intheapexof the gonad inother

68 SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95 forms is, therefore, as

Willem

contends, a specialized condition; it results intheformationof agonad resembling a single testicularor ovarialtube of

Thysanura

andPterygota, butwhich cannotbe a

mor-

phological counterpart of the latter, since the tubes of a

compound

gonadare developedaslateral outgrowthsof the primitivesac.

The

developmentof the eggs intheovary of

Podura

isdescribed by

De Winter

(1913),

who shows

thatthe oocytes are proliferatedin rows extending peripherally

from

the germarium, andthat they be-

come enmeshed

in a reticulum of ^cells that

grow

inward

from

the outer epithelium of the ovary.

The

distaloocytes, byreason of their closer contact with the blood, are the better nourished and develop into the functional ova, while the

more

central cells

become

degen- erate,and

some

of

them

incontact withthe outer cells areabsorbed by the latter.

The

general structure of the ovary of Podura, with the peripheral development ofthe ova, andthe close resemblanceto theovaryof Lithobius,

De Winter

contends,showsthatthepoduran ovary is not derived by condensation or reduction

from

the

com- pound

type ofinsectgonad,but isagonad of generalized structure, and represents the most primitive type of ovary found

among

the insects.

No

verified observations haveyetbeen

made

ontheexact

manner

of insemination of thefemale bythemaleinCollembola.

The

curious matinghabits of the Sminthuridae, however, have long been

known

and haverecentlybeendescribedin detailby Falkenhan (1932) and by Strebel (1932).

The

male approachesa femaleand withhisantennae grasps theantennae of the female, the male antennaebeingspecially adapted for claspingby a modification of the second and third seg- ments.

The

maleis thenliftedbythefemale,

who

carries

him

around suspendedbefore oraboveherbodywhile she goesabouttheaffairsof her ordinary life.

The

male remains inactive with his legs folded against thebody,andisthustransportedbythefemalefor a time vary- ing

from

afew hourstoaslongasadayandahalf,butwithintermis- sions the carrying of themale

may

be continued for four orfivedays.

Only

onewriter, Lie-Pettersen (1899)^,claimstohave observedtheact of insemination;accordingto hisaccount amalewhile suspended by thefemale

was

seentoemit adropof spermaticfluid,whichfellonthe wall of the glass tube containing the insects,

whereupon

the male released himself, with his fore legs smeared thedrop on his

mouth

parts, and then inserted the latter into the genital opening of the female. NeitherFalkenhan norStrebel,after prolonged observation, saw any act on the part of the mated sminthurids such as that de- scribed1)yLie-Pettersen. Falkenhanpostulates,however,that insemi-

NO. 14 INSECT

ABDOMEN

SNODGRASS 69 nation

may

take place bythe emission of a drop of spermaticfluid fromthe male, which, falling totheground,is taken

up

directly by the femaleintohergenitalorifice. There seemstobelittledoubtthat themating performanceof theSminthuridaeisaccessorytoinsemina- tion, since Falkenhan finds that the eggs of females that have not beenallowedtomateare infertile.

Egg

laying takes place ordinarily about14to 18daysafter mating,thoughthe time varies accordingto temperature and theage of the female.

The

Protura, in the fully matured stage, have 12 abdominal seg- ments, and this character would appear to relate

them more

closely to insects other than Collembola, in whichthe

maximum

segmenta- tionof theabdomen,as

shown

intheembryosof

some

forms,consists of eleven somitesandatelson.

The

^{Proturadififer}

from

otherhexa- pods in that thelast

two

somites before theend segment, or telson, are formed during postembryonic growth, as in anamorphic Chi- lopoda.

Whether

segmentationiscompletedbefore or after hatching, however, cannotbe amatter of great importance, sinceit is variable

among

thechilopods themselves.

The

genitalopeningsof theProtura areon^thepenultimatebody segmentasinCollembolaand Chilopoda, but, asalreadypointedout, thegenital segment, though subterminal in position, is numerically quite a dififerent somite in each of these threegroups.

The

gonads of Proturalie ventral to the alimentary canal, asin Collembola, but in their structure they resemble a single gonadial tube ofaninsectovaryortestisof the usual

compound

type, inwhich each tube has a germarial zone at its apex.

The

proturanovaryor testis,as describedby Berlese (1910),isa large tubular sac withthe tapering anteriorendfolded ventrallyandposteriorly. In the deflexed apical region are contained the oogonia or spermatogonia, and the restof the tubeisoccupiedbythedeveloping oocytes or spermatocytes.

The

oocytes arearrangedina singleseriesendingwith amature

ovum

as in an ovariole of other insects, and the successive stagesof the maturing spermatozoa

form

zones ofgrowthasinanordinarysperm tube.

The

proturan gonadthus does nothavethe primitive or gener- alizedstructureof a collembolan or chilopodgonad,andits simplicity of form, therefore, would appearto be the result of elimination of tubes

from

a

compound

organ,as is probablythecasealso incertain Diplurainwhichthegonadconsists likewise of asingle egg tube or spermtube.

The

vasa deferentia of Protura discharge individually through terminal ejaculatory ducts, but the oviducts

come

together ina shortmedianoutlet tube.

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SMITHSONIAN MISCELLANEOUS

COLLECTIONS VOL. 95