THE HORMONE THEORY 167 



host may be infected by the parasite, but the pres- 

 ence of the latter causes suppression of the somatic 

 sex-differences. The entry of the parasite is effected 

 when the crab is young and small, before the somatic 

 sex-characters are fully developed. The gonads are 

 not actually penetrated, at least in some cases, by 

 the fibrous processes of the parasite, but neverthe- 

 less they are atrophied and almost disappear. In 

 Inachus the abdomen of the normal male is very 

 narrow and has no appendages except two pairs of 

 copulatory styles. The abdomen of the female is 

 very broad, and has four pairs of biramous appen- 

 dages covered with hairs, the normal function of 

 which is to carry the eggs. The effect of the para- 

 site in the male is that the abdomen is broader, the 

 copulatory styles reduced, and biramous hairy 

 appendages are developed similar to those of the 

 female, but smaller. In the female the abdomen 

 remains broad, but the appendages are much 

 smaller than in the normal female, about equal in 

 size to those of the ' sacculinised ' male. Smith 

 interpreted the alteration in the male as a develop- 

 ment of female secondary characters, but it is 

 obvious from the condition in Macrura or tailed 

 Decapods, like the lobster or crayfish, that the ab- 

 domen or tail of the male originally carried appen- 

 dages similar to those of the female, and that the 

 male character is a loss of these appendages. The 

 absence of the male character therefore necessarily in- 

 volves a development of these appendages, and there 

 is not much more reason for saying that the male 

 under the influence of the parasite develops female 

 characters, than for saying that the male character 

 is absent. There is no evidence in the facts con- 



