278 



ENTEMAN. 



[Vol. II. 





Let us consider next the derivation of the terminal portion 

 of the genital ducts. We rely here on some evidence of a 

 more indirect character, but even then, it seems to me, the 

 relations can hardly be questioned. In all the insect orders, 

 with the exception of the male Ephemerids and some of the 

 Dermaptera, the paired genital ducts open on the exterior 

 through an unpaired terminal portion. This unpaired terminal 

 portion arises independently from the integument, and during 

 development comes into relation secondarily with the paired 



portion. It may be exceed- 

 ingly slight in extent, as 

 in the female Ephemerid, 

 where it is merely a shal- 

 low depression between 

 the seventh and eighth 

 abdominal segments, the 

 ovivalvula, as it is called, or 

 it may be highly differen- 

 tiated, as in the Dipteron, 

 CallipJiora crytJirocepJiala, 

 where, according to Briiel, it includes in the male the seminal 

 vesicles and the ductus ejaculatorius, and in the female the 

 uterus, vagina, and vulva. Palmen ('84), in a series of sketches, 

 has shown the varying limit between the parts of mesodermal 

 and of ectodermal origin. These figures have been so exten- 

 sively copied in text-books that I deem it hardly necessary 

 to reproduce them here. 



The position of the external genital openings is very various. 

 In Chilopoda it is terminal in the last segment. In the female 

 Pauropiis it is near the posterior border of the second post- 

 cephalic segment ; the male apertures are paired, and the 

 reproductive organs are otherwise so aberrant as to be hardly 

 available for purposes of comparison. In most Hexapods the 

 male aperture is between the ninth and tenth, the female 

 between the eighth and ninth abdominal segments. In the 

 Ephemeridea and some Orthoptera {Blatta and Xiphidiiim) the 

 female opening lies behind the seventh segment. This insta- 

 bility in the position of the reproductive openings has been used 



Fig. 5. — Sagittal section of the nerve cord of Xiphi- 

 diuiii ensiferum a little to one side of median line. 

 (After Wheeler.) i-s-' y i-S--, first and second inter- 

 ganglionic depressions; ?«.«.^., median cord neuro- 

 blasts; in.x.gJ, first maxillary ganglion; vi.x.g.- 

 second maxillary ganglion ; c.nt., median cord. (?) 



