232 THE AMERICAN NATURALIST [Vol. LIV 



Parasitized females do not assume any of the features 

 peculiar to the males. 



The gonads in both sexes usually degenerate, and an 

 accumulation of fat takes place in the abdomen of the 

 host. Two exceptional cases have an important bearing 

 on the cause of the changes resulting from the parasitism. 

 One male was found that had been parasitized, and al- 

 though it had been considerably changed towards the 

 female in its somatic characters it "contained full-sized 

 normal testes with many spermatozoa." Evidently then 

 the changes caused by the parasite are not due directly 

 to the destruction of the gonads as shown by this indi- 

 vidual in which the gonads had escaped. This accords 

 with the results of artificial castration in other insects. 



The other exceptional case (fourth instar) had a ! 1 per- 

 fect female soma" but contained testes. The individual 

 had started as a female. There was evidence of this, 

 though it is not conclusive, in the chromosome counts of 

 the somatic cells. It must be supposed that at an early 

 stage something changed the cells of the germ-track, so 

 that its cells developed into testes. This conclusion is 

 borne out by a count of the chromosomes of the testes 

 that show 21 cells in the spermatogonia, one of them 

 being the largo X chromosome characteristic of the male. 

 An early "elimination" (loss) of an X chromosome from 

 the mother cell of the germ-track, such as occurs in Dro- 

 sophila, would seem to be the simplest explanation of 

 this case, as suggested by Kornhauser. 



The conclusion from the evidence is quite convincing, 

 namely, that the several characters peculiar to the male 

 are changed into those peculiar to the female as a result 

 of the direct action of the parasite, and not through any 

 influence by way of the gonad. 



Feeding Fiddler Crabs on the Genital Glands of the 

 Opposite Sex 



During the summer of 1918 I carried out some feeding 

 experiments. The occurrence of hormones in the repro- 



