6S8 



may not be attributed to individual variation between the first and 

 second form. Size of testis as a whole, number of mature elements 

 present, stage and number of spermatids, and mitotic activity seem to 

 be the same w^hether the testis comes from first- or second-form. 



In the spring, as in the late summer, the condition of the testes 

 of first- and second-form show practically the same condition: a proxi- 

 mal area of emptied follicles followed by one in which they contain 

 apparently the original number of mature spermatozoa with an occa- 

 sional follicle containing spermatocytes in fine speremo condition, se- 

 parating the area of spermatozoa from the distal spermatogonial region, 

 where occasional division figures are to be observed. The vas deferens 

 is well filled with spermatozoa, retaining them for several days after 

 the animal has passed from first to second form. 



The above described lot of material tends to show that the main 

 part of the regeneration of the male sexual elements takes place be- 

 tween the spring exuviation, in which the animal assumes the second 

 form, and late in August, during the latter period of which time the 

 animal may be in either of the forms. 



While advancing this theory rather tentatively it seems to me 

 that from the evidence at hand we must conclude that the second-form 

 represents the period in each years life of the adult individual in which 

 the greater part of the regeneration of sexual elements takes place, 

 but that the limits of this period are very indefinitely fixed. In other 

 Avords the sexual condition of the male is not the only factor to be 

 taken into consideration, as is well shown by the variation observed 

 in the testes of individuals in the same form as well as by the occur- 

 rence of individuals in which the alternation of forms does not occur 

 regularly. 



Our present knowledge of the Dimorphism in the males of Cam- 

 harus may be briefly summarized as follows: 



1) The Alternation of Forms which Faxon observed for C. rusti- 

 cus Girard and C. propinquus Girard has been shown for C. immunis 

 Hagen and without doubt occurs in C. virilis Hagen. 



2) Exceptions to this Alternation of Forms are to be found in 

 adult individuals. 



3) No difference can be detected between the testes of first- and 

 second-form males taken at the same time of year either as regards 

 gross anatomy or microscopic structure, as far as the presence of the 

 sexual elements is concerned, therefore, the second-form male is as 

 capable of copulation as is the first-form. 



4) The second-form condition probably represents in the adult 



