62 INTERNAL SECRETIONS 



like the fissipedes. The claw of the male becomes smaller, the 

 abdomen broader. In this way the infected males become 

 more or less female in their external appearance {Figs. 41 and 

 42). They sometimes resemble normal females so closely 

 (Figs. 43 and 44) that they can be recognised as modified males 

 only by the reduced copulatory organ and the sHghtly smaller 

 abdomen. On the contrary, the infected females are only 

 slightly altered {Fig. 45). They differ from normal females 

 only by the shorter fissipedes, and they never assume male 

 characters. 



In 70 % of the male and female Inachus in which changes 

 in the external sex characters were present. Smith found also 

 changes in the sexual glands. In the female-like males Smith 

 found the sexual glands destroyed to such a degree that even 

 by serial sections no remains of a sexual gland could be found. 



A further instance of parasitic castration in crabs is afforded 

 by Pachygrapsiis marmoratus likewise investigated by Smith in 

 Naples. Here also the castrated male approaches the female 

 in its appearance. The results of castration, however, are not 

 all equally marked in the different species of crabs, the change 

 towards the opposite sex being much more pronounced in 

 some than in others. In some the male sexual characters 

 remain unaltered notwithstanding castration. 



The results of the observations made on Inachus could be 

 conceived at first sight as similar to those with birds, which 

 after castration change more or less to the male type. But in 

 Inachus the change takes place from male to female, and not 

 from female to male as in birds. Like the castrated cock, the 

 castrated female Inachus shows only slight changes in the 

 external sexual characters. We have interpreted the assump- 

 tion of male sexual characters by the castrated hen as of the 

 nature of an approach to an " asexual " or neutral form common 

 to both sexes, and not as an inversion to the other sex. We 

 may in the same way interpret what we observe in Inachus, 

 supposing that the common neutral form in this animal 

 resembles the female rather than the male. The absence of 

 fissipedes in the normal male of Inachus and their appearance 

 after castration might be explained in the following manner : 

 there is normally an inhibition exerted by the male sexual 

 gland upon other parts of the body, and this inhibition is 

 removed by castration. A similar explanation may be adopted. 



