The second valvifers belong to the ninth abdominal segment, and are provided with muscles arising on the ninth tergum. They are

42 SMITHSONIAN MISCELLANEOUS 89

4. The second valvifers belong to the ninth abdominal segment, and are provided with muscles arising on the ninth tergum. They are

alwayslocatedbetweentheloweredges of thetergum andthenarrow medianventer of the ninth segment.

The

second valvifers,together with the third valvulae, correspond with thestylus-bearingplates of theninth segmentof Thysanura, andaretherefore derived

from

the

NO. O INSECT

ABDOMEN

SNODGRASS 45 bases of the secondgonopods. Inmostpterygote insectseachprimi- tive limb base of the ninth segment becomes differentiated into a proximal second valvifer, and a free distal lobe, or third valvula.

In

some

of the lower insects the third valvulae bear small terminal styli,whichareusuallylost inthe adultstage.

5.

The

^third valvulae are secondary differentiations of the limb bases of the second gonopods, formingfreelobesatthedistalendsof the second valvifers. Usually they ensheath the distal part of the ovipositor between their apposed inner surfaces, but in most of the Orthoptera they resemble the gonapophyses, and

form

a third pair of bladesintheshaft of theovipositor.

6.

The

intervalvularscleritesare remnants of the ninthabdominal sternum^; in

some

insects they give insertion to tergosternal and other muscles.

DEFINITIONS

The

followingtermsappliedtothe ovipositorandassociatedstruc- tures are here defined as used in this paper in order to

make

the applicationclear, andto avoid the confusions of synonymy.

Oviductiislaterales (Odl).

— The

paired oviducts,

formed

primarily

from

themesodermalstrandscontinuouswiththemesodermalsheaths of the ovaries,buttheirposteriorparts

may

beof ectodermalorigin,

and

in

some

cases theentiremesodermal ducts are saidtobe replaced byectoderm.

The

ducts areattachedtotheectodermatthe posterior border of theseventhsegment in

young

stages of

many

insects,and open at this position inadult Ephemerida,but in other adult insects they are confluentintheanteriorend of the

median

oviduct.

Oviductus

communis

(Ode).

— The

medianoviduct, of ectodermal origin, opening in

Dermaptera

just behind the seventh abdominal sternum, butinotherinsectsextendedtotheeighthsegment.

Female

gonopore (Gpr).

— Any

of the true oviducal apertures, paired or median.

The

paired gonopores of

Ephemerida

and the median gonopore of

Dermaptera

are on the posterior part of the seventh abdominal segment;the singlefemale gonoporeof otherin- sectsis

on

or just behindthe eighthsternum,

where

it is either ex- posed externally or concealed in the genital

chamber

(copulatory pouch, or vagina).

Spermatheca, receptacidum seminis (Spt).

— An

ectodermal in- vagination, usually single, but often double,

and

sometimes triple, serving for the reception of thespermatozoa;primarilyformed onthe posterior part of the eighth abdominal segment, opening into the anterior end of the genital chamber, or vagina,

when

this organ

ispresent.

46

Accessory glands (AcGl).

—

^{Typically a bifurcate or paired in-}

vaginationontheventer of the ninthsegment,usuallyformingglands havinga coUeterial function.

Gonopods

(Gp).

— The

appendages of the eighth and ninth ab- dominalsegments.

Each

gonopod,

when

complete, consists of abasis (Lb) bearing a proximal, medial gonapophysis (Gon), and a distal stylus (Sty).

Ovipositor(Ovp).

— The

egg-layingorgan

formed

of thegonopods.

First valvifers (iVlf).

— The

basalplatesor lobes of the ovipositor supporting thefirstvalvulae;derived

from

thebases of thefirstpair ofgonopods, and providedv^^ithmusclesarisingonthe eighthtergum.

Second

valvifers {2Vlf).

— The

^basal plates or lobes of the ovi- positorsupportingthesecondvalvulae^;derived

from

thebases of the second gonopods,

and

provided with muscles arising on the ninth tergum. (Usuallycalled "coxites" of the ninth segment.)

First valvulae (iVl).

— The

gonapophyses of the first gonopods, formingthe ventral blades of the ovipositor.

Basivalvulae (bv).

—

^{Smallsclerites sometimes}differentiatedatthe bases of thefirstvalvulae.

Second

valvulae (2VI).

— The

gonapophyses of the second gono- pods, forming usually the dorsal blades of the ovipositor, but the inner bladesinOrthoptera havinga third pair of valvulae.

Third valvulae (3VI).

— The

distal lobes of the second valvifers, derivedwiththelatter

from

thebases of thesecond gonopods;usually forminga sheath for the shaft of theovipositor,butinmost Orthop- teraa third (dorsal) pair of bladesintheovipositor.

Intervalvulae (iv).

—

^Sclerotic remnants of the ninth sternum be- tweenthesecondvalvifers.

Egg

guide.

— A

medianprocesssometimespresentontheendof the eighthsternum behindtheinvaginatedgonopore,servingto directthe eggsintothe channel of the ovipositorbetweenthebases of the first valvulae.

Genital

chamber (GC). — An

inflectionof thebodywallatthebase of the ovipositorabovetheendof theeighthabdominalsternum,form- ingapouchcontaining thegonopore andtheopening of thesperma- theca;inPanorpidaethegenital

chamber

is closedbelow bythe ninth sternum and opens abovethelatter.

Vestibulum (Vst).

— A

cavity

formed

byinflectionof thebodywall above the seventh sternum

when

the latter is prolonged beyondthe eighth, thus concealing the true genital

chamber

above the usually reducedeighthsternum.

NO. 8 INSECT

ABDOMEN —

SNODGRASS 47 Suhgcnital plate.

— The

exposed sternal plate beneath the genital apparatus; primarily the eighthabdominal sternum, but theseventh

when

the latter underlies

and

conceals the reduced eighth sternum, or the ninth sternum

when

the vaginal openingis transferredto the ninthsegment.

Vagina (Vag).

— The

^genital

chamber when

^the latter takes on ^a pouchlike or tubular

form

withanarrowedposterioropening;in

some

insects extended into the ninth segment to open on or behind the ninth sternum.

Ostium

vaginae, or vulva (Vul).

— The

external opening of the copulatory pouch or vagina, on either the eighth or the ninth ab- dominal segment, serving usually both for copulation and for the discharge of the eggs.

Bursacopulatrix.

— ^Any

cavity of the femaleserving for the recep- tion of themale organ of copulation;usually thegenital

chamber

or itsderivative, thevagina;inmost Lepidoptera adiverticulum of the genital

chamber

invagination on the eighth abdominal segment.