290 GENETICS 



8. THE EFFECT OF PARASITISM ON SEX 



It has been well demonstrated in insects that castra- 

 tion, even of very young individuals, produces no effect 

 upon the secondary sexual characters when the animal 

 reaches its adult form. Even the implantation of 

 gonads of the opposite sex results in no change. The 

 growth and development of the soma seems to be fixed 

 by the chromosomal complex and does not appear to 

 be influenced by the action of any sex-hormone. Altera- 

 tions of secondary sexual characters may occur, how- 

 ever, by means of parasitism, as shown by experiments 

 on Crustacea and insects. 



Among Crustacea the best case of this kind per- 

 haps is that of the crab Inachus, the male of which 

 when parasitized by the cirripede Sacculina, as de- 

 scribed by Smith, becomes similar to the normal female 

 in the form of its claw, abdomen and abdominal ap- 

 pendages. 



Among insects Thelia bimaculata, described by Korn- 

 hauser, is a good example. Parasitized males resemble 

 females even to the minute structure of their chitinous 

 integument. Such alterations are due, very likely, to 

 an entire upset in the metabolism of the host, changing 

 the internal environment so fundamentally that the 

 genes for the male secondary sexual characters fail to 

 find the conditions necessary for their expression in 

 the developing soma. 



9. GYNANDROMORPHS AND SEX INTERGRADES 



In insects and Crustacea abnormal individuals occa- 

 sionally appear, presenting both male and female 



