50 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 The gnathochilarium has been variously regarded as representing

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J -^^QL^K L

Fig. 19.

—

Diplopoda: externalgenitalia.

A, Habrostrepus, male, sternum, legs, and penes of third body segment, posterior view. B, same, gonopods, anterior (under) surface.

_C, Eurynrns, male,sternum,legs,andpenesof thirdbody segment, anterior view. D, same, seventh body segment, ventral view, showing position of gonopods and legs.

E, same, right gonopod, anterior (upi^r) surface. F, Parajulns impressus, female, ventral partof thirdbody segment andappendages, anterior view,telop- odite of right appendage removed exposing gonopore on the coxopodite. G, Thyropygus, male, rightgonopod, anterior (under) surface. H,same, penes, posteriorsurface. I,same, leftgonopod, posterior (upper) surface. _J,Para-

iuliisimpressus, male, third body segment and appendages of secondsegment, posteriorview. K,same,appendagesofsecondbodysegment, posteriorsurface.

L,same,sternum and firstgonopodof seventhbody segment, anteriorsurface.

M,same, second gonopods, posterior ^surface.

Ap, apodeme;c,spermcanalofgonopod;cxl,coxal lobe;Cxnd,coxalendite

;

Cxpd, coxopodite; Gpr, gonopore; iL, first leg (on second body segment);

2L, secondleg (onthirdbody segment); 9L, ninth leg (second leg ofseventh body segment); Od,oviduct;Pen,ijenis; r,sperm receptacleofgonopod; Stn, sternum; T,tergum^;Tlpd,telopodite.

SI

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ment

(fig. 19 C,F).

The

male ducts usually discharge separatelyon a pair of,small penes having the

form

of papillae or lobes arising either directly

from

thecoxaeof thesecondlegs (C,Pen),or mesally behindthe coxal bases(A),butin

some

formstheductsopentogether

on

amedianpenis arisingbetweenorbehind thelegs (J,Pen).

The

legs of the genital segment in most cases have the typical leg

form

(A, C),but they

may

bereducedin size and otherwise modified, or unitedat their bases _(J,

Cxpd).

In certain species thefirstlegsalso are modified in a

manner

suggestive that they take

some

part in copulation _(J, iL,

K).

The

female genital ducts open either onthe coxaeof the legs of thegenital segment, oronthe sternal surfacebehind the legbases.

Usuallythelegsof thegenitalsegmentare not modifiedinthe female, but there are exceptions, as

shown

inParajulusimpressus(fig.19 F), inwhichthe telopodites of thegenitalappendagesarereducedto small lobes {Tlpd) and the oviductsopen into largecavitieson extensions of the united coxopodites {Cxpd). Informsinwhichtheductsopen behind thelegs, the apertures are usually containedina complicated integumental structure (see

Brolemann

and Lichtenstein, 1919, and Seifert, 1932).

Intromission is accomplished in the ordinary diplopods (Proter- andria) bythe modifiedlegs (gonopods) of the seventhbody segment of the male,whichtransfer the

sperm from

thepenesor penis of the third segmentintothegenital apertures of the female. Intwoof the diplopod groups, however, the relativelygeneralized Pselaphognatha andthe Opisthandria,accordingtotheclassificationof

Attems

(1926)

,

noneof the appendagesismodified for thepurposeof intromission, though in

members

of the first group the coxaeof the eighth legs haveexternal pouches,which

Attems

suggests

may

have

some

repro- ductive function. In the Opisthandria oneor

two

pairs oflegs atthe posteriorend of the

body

inthemaleare specially modifiedtoserve as copulatory organs.

With

theselegs the male is said to grasp the genital coxae of the female, while he inserts the spermatozoa into the female gonopores with his mandibles (Attems, 1926).

The

gonopods of the seventhbody segmentof proterandriousmale Diplopodaare analogous in their function to the gonopods of mala- costracanCrustacea

and

the pedipalpsofmalespiders;in their struc- ture even they are not dissimilar from these organs.

The

^pair of appendages converted into gonopods is usually the first pair of legs of the seventhsegment;thesecondlegsof thissegmentare generally of usual form, but they

may

be absent, or modified also to

form

a second pair of gonopods.

A

typical diplopod

gonopod

^(fig. 19

E)

NO. 14 INSECT

ABDOMEN

SNODGRASS ₅₃ consists of two segments, a basal coxopodite (Cxpd), and a distal telopodite {TIpd).

The

essential feature of the organ is a

sperm

receptacle (r),whichisaninvagination cavity

on

themorphologically anterior surface of thecoxopodite, and a

sperm

canal (c),which is usually a closedgroove thattraverses the telopodite

from

the sperm receptacletotheapexof theappendage.

The

coxopoditeisgenerally providedwithamovableendite lobe

(Cxnd)

of various shapes,which projectsover the

sperm

receptacle,and

when

slender

may

be partly insertedintotheproximal openingof thespermcanal.

The

bases of the appendages are often sunken into a deep cavity on the ventral surface of thebody segment (D).

The

gonopodsare subject to end- less modifications in form, andtheir structural diversityin different generaandspeciesfurnishesvaluable charactersindiplopodtaxonomy.

An

example of gonopods having a highly diversified

and complex

structureis

shown

in thegenus

Thyropygus

(fig. 19G, I).

A

^very

much

simplified structure, on the other hand, is found in

Habro-

strepus (B), in which the telopodite (Tlpd) of each

gonopod

has the

form

of a short broad lobewith a wide, basinlike sperm cavity (r) onitsventral anterior surface, whichispartlycoveredby aflat endite lobe (Cxi) of the coxa. In

some

forms, as in Parajtdus (L,

M),

bothpairs of legs of the seventh body segment are trans- formedinto gonopods, the second of whichin this case contain the sperm receptacles

(M,

r) and canals (c).

More

extensive andde- taileddescriptions of the diplopodgonopodswill be found in

works

by Vosges (1878), Verhoeff (1903),Silvestri (1916), Attems(1894, 1926), and Siefert (1932)^{;the last}writer gives alsoan accountof the

manner

of copulationand inseminationin

Polydesmus

edentidus.

IX.

CHILOPODA (MYRIAPODA OPISTHOGONEATA) The

Chilopoda have a single median genital aperture, which in each sex is always behind the sternum of the last somite, that is,

betweenthe penultimatebody segment andtheanus-bearingend seg- ment, or telson.

The number

of segments anterior to the genital segment, however, is so variable inthe chilopods as a wholethat no fixednumericaldesignationcanbe giventothegenitalsegmentitself.

In the anamorphic forms (Lifhobius, Scutigera), inwhich the adult segmentation does not vary, there are 19 definitive body segments, including thetelson. Counting four postoral somitesin thehead, the genitalsegment inthisgroup, therefore,issomite

XXII

^.

Among

the Epimorpha, in which the definitive segmentation is in most forms complete at hatching, the

number

of segments is highly variable in theGeophilomorpha, eveninthe

same

species,and

may

be verylarge,

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