THE EFFECTS OF CASTRATION 155 



The difference in color can be shown, in fact, to be 

 due to this quantitative relation. If, for instance, an 

 eosin female is mated to a white-eyed male, her 

 daughters have light eyes exactly like those of the 

 eosin male. The white-eyed fly lacks the eosin factor 

 in his sex chromosomes (as suitable matings show), 

 hence the hybrid female has but one dose of eosin, 

 and in consequence her eye color becomes the same as 

 the male. 



In this case a sex-linked character is also a secondary 

 sexual character because it is one of the rather unusual 

 cases in which a factor in two doses gives a stronger 

 color than it does in one dose. 



PARASITIC CASTRATION OF CRUSTACEA 



Let us turn now to a group in which nature performs 

 an interesting operation. 



Giard first discovered that when certain male crabs 

 are parasitized by another crustacean, sacculina (a 

 cirriped or barnacle), they develop the secondary sexual 

 characters of the female. Geoffrey Smith has confirmed 

 these results and carried them further in certain re- 

 spects. Smith finds that the spider crab, Inachus 

 mauritanicus, is frequently infected by Sacculina neglecta 

 (Fig. 79). The parasite attaches itself to the crab and 

 sends root-like outgrowths into its future host. These 

 roots grow like a tumor, and send ramifications to all 

 parts of the body of the crab. 



The chief effect of the parasite is to cause complete 

 or partial atrophy of the reproductive organs of the 

 crab, and also to change the secondary sexual charac- 

 ters. Smith says that of 1000 crabs infected by 



