186 CALIFORNIA ACADEMY OF SCIENCES. 



however, in the basal half of the organ, the inner lay- 

 ers of the tunicas are absent and the opposing cells 

 fused. The ejaculatory duct (plate xiii, fig. 4) has the 

 same structure as the seminal vesicle and vasa defer- 

 entia. Outside of its tunica, however, is a layer of 

 circular muscle fibers. These continue a short distance 

 over the base of the seminal vesicle (plate xiii, fig. 5) 

 and unite the lower ends of its lobes more firmly, but 

 they soon cease. 



From the preceding descriptions it is evident that 

 figure 4, on page 177, represents the typical development 

 of the internal genital organs of the males for the 

 whole order. The only constant difference between the 

 two orders in respect to these organs is the number 

 and relative position of the testes. The latter organs 

 have no constant form in the Amblycera although the 

 variation is small, while on the other hand, in the 

 Ischnocera the form is almost entirely constant. Thus, 

 with respect to the sperm glands, as was found to be 

 the case also with the salivary glands, the Ischnocera 

 are specialized as a group, while the Amblycera are 

 specialized among themselves on a less evolved type. 



It now remains to consider the nature of the struct- 

 ure referred to as the vesicula seminalis. As stated, 

 Kramer regarded it as an accessory gland, but he 

 did not siiow what its function as a gland is. He 

 found, further, that the spermatophores are not formed 

 in the male ducts, but in the female spermathseca. 

 That it is composed of united right and left organs is 

 very evident. This is indicated by the fact that it is 

 actually entirely divided into two lateral lobes in at 

 least one form, and in others it is more or less deeply 

 cleft, while in none known is it without a median groove. 

 Further, according to Nusbaum (1882), it actually 



