64 KANSAS UNIVERSITY SCIENCE BULLETIN. 



THE DIMORPHISM OF CAMBARUS. 



The consideratioa of the very remarkable condition of a sex- 

 ual dimorphism in the adult males of Cambarus is within the 

 scope of the present paper in so far as it is connected with the 

 breeding habits of the animals. The taxonomic importance of 

 the existence of the two forms was pointed out by Doctor Hagen 

 ('70) and has been since confirmed for every species of which 

 a large series of males has been examined. Doctor Faxon 

 ('846) announced the true nature of the dimorphism as an al- 

 ternation of forms in the individuals. Harris ('01?> and '01c) 

 confirmed Faxon's observations on a much more extensive 

 series of material, finding that there are apparently exceptions 

 to the rule of the alternation of the two forms in the adults, 

 and made a cytological study of testicular material, showing 

 that when the season at which material is secured is taken into 

 consideration no marked difference in the essential reproductive 

 organs of the two forms is observable. In C. immunis, and 

 perhaps in C. virilis as well, the proportion of first-form males 

 gradually increases in late summer and autumn, there being, so 

 far as he could determine, no definite time for exuviation. 

 In the spring the animals appeared in the open water early in 

 March and all males taken up to April 15 were first-form, but 

 in a very short time afterward nearly all the males had assumed 

 the second-form condition. His study of a series of testes led him 

 to the conclusion that so far as the presence of sexual elements 

 is concerned the second-form is as capable of copulation as the 

 first-form, and that in the adult the second-form condition prob- 

 ably represents the period in which the regeneration of the 

 sexual elements for the most part takes place. He also points 

 out the parallel between the alternation of forms in Cambarus as 

 secured by spring and fall exuviation and the spring and au- 

 tumn exuviation in the male of Astacus as described by Euro- 

 pean observers. 



Hagen and Faxon considered that the second form is prob- 

 ably sterile, and the rudimentary condition of the external male 

 organs, the pleopods and hooks on the legs (for a discussion of 

 the function of these, see the section on conjugation) would 

 certainly suggest this view, but the work on the microscopic 

 structure of the testis leaves no doubt as to the presence of the 

 spermatozoa in the same quantity, and apparently in the same 



