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THE AMERICAN NATURALIST [Vol. LIV 



other Decapods parasitized by other crustataceans (Sac- 

 culina Portunion, Pelto<iasier, etc.), in which changes 

 take place in certain parts of the body that approach the 

 condition found in the opposite sex. These changes in- 

 volve most often the abdomen and its appendages, and 

 in one species at least the claws. The most marked 

 changes involved the male, producing in him alterations 

 in the direction of the female. In one case a female is 

 described as showing some effects of the parasite but if 

 I am correct Giard interpreted this change as resulting 

 from the retention of the juvenile condition. Giard con- 

 trasts the changes in the male crabs with those produced 

 by castration in the vertebrates. He seems to imply at 

 times that he supposed the effects are produced by the 

 loss of the gonads. At other times, however, he speaks 

 definitely of the changes as some sort of symbiotic rela- 

 tion between the host and the parasite— an idea similar 

 in many respects to the later and more elaborated hy- 

 pothesis of Geoffrey Smith. In fact, in summing up the 

 evidence Giard recognizes two classes of cases; those 

 due to the indirect action of the parasite by way of the 

 testes, and those due to the direct, by action on the host. 

 It was, of course, at that time natural to suppose that in 

 both groups, vertebrates and crustaceans, castration acts 

 in the same way, especially as the case of the vertebrates 

 had been long in the literature, and zoologists had be- 

 come familiar with this kind of effect. Moreover at the 

 time other evidence was lacking to show in other groups 

 that the gonads have no influence on the development of 

 the secondary sexual characters. But the work of Oude- 

 manns that was later fully confirmed and extended by 

 Kopec and by Meiscnhoimer and by Kellog removed any 

 prejudice that the situation in the vertebrates had 

 brought about, so that at the time when Geoffrey Smith 

 wrote the field was clear for an independent judgment. 

 As stated Geoffrey Smith brought forward evidence that 

 seemed to him to show that the changes in the secondary 

 sexual characters in parasitized males were due to physio- 



