230 M. E. Haase on the 



mation of the abdominal segments is rendered possible we 

 may also take our Cockroaches. 



In the almost completely developed embryo still enveloped 

 in the egg-membranes (without the branchiiform appendages 

 of the first ventral segment) a diminution of the number of 

 the abdominal segments results from the tenth being sup- 

 pressed, first ventrally and then dorsally, and, as was first 

 demonstrated by Cholodkovsky *, finally having its dorsal 

 plate amalgamated with the anal opercular plate |, when it 

 is still recognizable in the adult male. Subsequently the 

 occurrence of sexual maturity exercises an influence upon the 

 last four segments, inasmuch as the tenth especially appears 

 to be completely aborted in the female. The anterior nine 

 dorsal plates remain in both sexes distinctly developed, rather 

 less so certainly in the females, only the eighth and ninth are 

 retracted somewhat under the seventh dorsal plate. While 

 in the males the nine ventral plates remain developed until 

 maturity, in the females the eighth plate first retreats over the 

 seventh into the body and gradually becomes soft-skinned ; 

 then the ninth plate also passes into the body and over the 

 seventh ventral plate ; in Periplaneta the latter, having the 

 middle of its hinder margin cut off by paired notches, finally 

 grows into a shovel-like process which projects beyond the 

 posterior segment and applies itself to the anal valves J. 

 Thus in the mature females probably of all Cockroaches nine 

 dorsal plates, but only the first seven ventral plates, are recog- 

 nizable. By the retreat of the female sexual aperture, situated 

 in the eighth ventral plate, a considerable space — the genital 

 pouch — is produced; this is formed chiefly by the extended 

 connective membrane between the elongated seventh and the 

 eighth ventral plate. This serves for the development of the 

 egg -cocoon which is retained by the internal appendages of 

 the posterior gonapophyses. 



A graphical representation of the divisions of the body of 

 the mature female Cockroach may be furnished by the fol- 

 lowing number-sketch, in which the numbers standing above 

 the line denote the dorsal and those beneath it the ventral 

 shields of the abdomen §: — 



+ + - 



Fr +1, 2, 3 ^^ 1—7, 8, 9, 10 



" e " d l' h »- 1-4^0 ' 



* Zeitschr. f. wiss. Zool. xlviii. (1889) p. 100. 



t L. 0. Miall and A. Denny ('The Cockroach/ 18815) inaccurately 

 characterize this plate (p. 68 &c.) as the tenth dorsal shield. 



J; These "podical plates" were regarded by Huxley as the terga of an 

 eleventh abdominal segment. 



§ Fr indicates the " frontal " and A the " anal piece. ' 



