24 ASTACID^. 



The sexual parts of the second-form males are so much less devel- 

 oped that it would be allowable to consider them as sterile. An ana- 

 tomical examination of the second-form males without articulation in 

 the first abdominal legs was not possible, as the materials were not 

 sufficiently abundant. 



As before stated, I surmise the presence of similar sterile females ; 

 which as viragoes show more of a male type. 



An anatomical examination of the females of Oambanis acutus and 

 Bartoni reveals some difference in the shape of the ovarium. 



Internal Sexual Parts of the Cambarus Female. Of C. acutus. Table II. 

 Fig. 123. — In Cambarus acutus the ovarium is nearly an inch in length, 

 elongated, narrow. The two superior lobes are shorter, cylindrical, a 

 little inflated at the base ; the inferior lobe is elongated, conical. The 

 connecting part is more enlarged, and gives on each side a large oviduct. 

 Above this part is situated a strong membrane, which passes with an 

 acuminated tip between the superior lobes ; it is provided laterally with 

 some bands of "musculi alati," while the fibres are strongly striated 

 transversely. This membrane also shows several nerves, apparently 

 belonging to the nervus sympathicus. 



Of C. Bartoni. Table II. Fig. 129. — In Cambarus Bartoni, 2 inches 

 in length, the ovarium is 0.65 inch long, and larger. The superior 

 lobes are shorter and oval ; the inferior a large cone. The oviduct is 

 even broader. The membrane is similar to that in Cambarus acutus. 

 In both species examined, the ovarium was filled with eggs of different 

 sizes and degrees of development. 



No Dimorphism in the true Astaci. — The existence of two forms of 

 males in the Cambarus of North America has been proved by me in all 

 species in which I was able to examine a large number of specimens. 

 In five species, represented only by single specimens of first-form males 

 or females, I have not seen the second form. But the existence of 

 this second form will be by far the more interesting, since it seems that 

 in the Astacidai only the Cambarus possesses two forms of the male. 

 I have examined nearly two hundred specimens of Astacus fluvialilis 

 from different European localities (Germany, Switzerland, France, Scot- 

 land), without finding a difference in the males. I must add that I 

 have not seen very young specimens, and do not know at all whether 

 the young have the first pair of abdominal legs articulated as in the 

 Cambarus. The smallest specimen seen by me is 1.5 inch long. Of 

 the Californian Astaci I have not seen more than a dozen males. All 

 these were quite full grown, and without any differences answering to 

 the second form of Cambarus. Of the Amur species I have seen but 

 one female. 



Dimorphism in other Crustacea. — Perhaps this fact of the existence in 

 the Crustacea of two forms, one always sterile, is not unique. In the 



