176 CALIFORNIA ACADEMY OF SCIENCES. 



external genitalia, in which the terms inte7'nal and exter- 

 nal are used relatively with regard to the adnlt structure. 



1. THE MALE ORGANS. 



The Internal Male Genitalia. — The testes are either 

 six or four in number in adults, the former number 

 being confined to the Amblycera and the latter to the 

 Ischnocera. In the Amblycera they are variously- 

 shaped organs lying in the lateral parts of the adom- 

 inal cavity, three on each side, one in front of the other. 

 Each opens by a short vas deferens into a common sperm 

 duct. In the Ischnocera the testes are two in number 

 on each side. They are generally pyriform, having the 

 pointed ends turned away from each other and each 

 terminated by one or two fine threads, and having the 

 blunt ends approximated and connected by a short, nar- 

 row commissure from which the common vas deferens 

 arises. The other internal reproductive organs of the 

 male are essentially alike in the two suborders. The vas 

 deferens on each side runs generally first backward from 

 the testis and then turns forward to enter the sperm ves- 

 icle. The latter organ is usually single, but is composed 

 of right and left lobes which in many cases are easily 

 separated and which are sometimes normally discon- 

 nected. In all cases their lower ends open into a com- 

 mon ejaculatory duct. This goes to the exterior and 

 may be either straight or variously bent. The two halves 

 of the sperm vesicle when not entirely separated exter- 

 nally are essentially distinct, since each half possesses 

 its own lumen, into which the vas deferens of the same 

 side opens. Figure 4, then, may be taken to represent 

 diagrammatically the typical condition of the internal 

 male genitalia of the whole order. The figure as it is 



