TEMPORARY HERMAPHRODITISM 



103 



This is well exemplified in the case of the ordinary males of 

 IiiacU-us mauritanicus, of some other Oxyrhynchous crabs, and 

 of the Crayfish Cambarus. 1 During the breeding season the males 

 of /. mauritanicus fall into three chief categories : Small males 

 with swollen chelae (Fig. 73, A), middle-sized males with flattened 

 chelae (B), and large males with enormously swollen chelae (C). 

 On dissecting specimens of the first and third categories it is 

 found that the testes occupy a large part of the thoracic cavity 

 and are full of spermatozoa, while in the middle-sized males 



FIG. 73. Iiiachus mauritanicus, x 1. A, Low male ; B, middle male ; C, high 

 male ; the great chela of the right side is the only appendage represented. 



with female-like chelae the testes appear shrivelled and contain 

 few spermatozoa. These non-breeding crabs are, in fact, under- 

 going a period of active growth and sexual suppression before 

 attaining the final state of development exhibited by the large 

 breeding males. This phenomenon is obviously parallel to the 

 " high and low dimorphism " 2 so common in Larnellicorn beetles, 

 where the males of many species are divided into two chief 

 categories, viz. " low males " of small size in which the 

 secondary sexual characters are poorly developed, and " higli 

 males " of large size in which these characters are propor- 



1 Faxon, Ann. May. Nat. Hist. (5), xiii., 1884, p. 147. 

 - G. Smith, Mitth. Zool. Stat. Neapel, xvii., 1905, p. 312. 



