204 CALIFORNIA ACADEMY OF SCIENCES. 



lateral pieces or not — embryology must decide this. 

 However, since the two are not known to be present in 

 the same form, and since in Goniodes cervinicornis, at 

 least there are non-articulated processes free from the 

 lateral walls of the penis, it might be inferred that the 

 two may be homologous. 



Comparison shows that the simplest forms of external 

 genitalia occur in the Amblycera, and that in none 

 of these are the parts much complicated. On the other 

 hand, the genitalia in nearly all the Ischnocera are 

 very much more developed, and are characterized by a 

 much wnder spreading of the chitin in the walls of the 

 penis, and of a relatively much larger development of 

 the internal process. The condition of the external 

 reproductive organs in the two suborders hence agrees 

 with that of the internal organs, for it was before 

 shown that the latter are the more specialized in the 

 Ischnocera. 



The structure of the intromittent apparatus of Menopon 

 titan will now be described (plate xiii, fig. 10, and plate 

 XV, figs. 2-5). It is so very highly developed and so 

 complicated, being much more so than in any other 

 form known, that it is more easily understood after a 

 study of the more typical structure found in other spe- 

 cies. Grosse has described it but apparently not very 

 correctly. He says that the last abdominal segment of 

 the male is invaginated and runs forward in the body to 

 the border of the last and penultimate segments, and 

 then goes again backwards in order to continue anew 

 anteriorly, tube-like, to the sixth segment. Surrounding 

 this are transverse muscles, and attached to its anterior 

 end longitudinal muscles. He next states that within 

 the invaginated segment is a tube open at both ends, 

 which anteriorly passes into a gradually decreasing 



