No. G32] SECONDARY SEXUAL CHARACTERS 231 



logical processes set up by the parasite in the host. He 

 even went so far as to compare directly and in detail the 

 substances called forth in the host by the action of the 

 parasite. Without discussing these questions here (since 

 I have recently discussed them in my paper on " The 

 Genetic and Operative Evidence Relating to Secondary 

 Sexual Characters," Carnegie Publication No. 285, 1919) 

 it is evident that crucial experiments must be made on 

 the crabs themselves before a conclusive case can be 

 made out. This is by no means a simple matter as I have 

 found. During the last three summers at Woods Hole I 

 have tried to carry out experiments on crabs to test some 

 of these questions. All attempts to remove the gonads 

 in fiddler crabs have failed, because of the delicacy and 

 distribution of the organs, and the fatalities that result 

 when the carapace is lifted up. Attempts such as Sta- 

 mati made in 1880 to destroy or injure the gonads by in- 

 jecting substances through the genital pores have also 

 failed, because of the delicacy of the tubes and the dis- 

 tance of the gonad, in the male, from the external genital 

 opening. 



Some important observations made by Kornhauser 

 (1919) on the effects of parasitism of the tree-hopper, 

 Thvlia b'nnacvlata, bv the hvmenopterom A tn ph eh >)>»■< 

 tJiHia have a bearing on the preceding discussion. The 

 egg of the parasite is deposited within the body of the 

 n\ limit of Thrlin from the first to the fifth instar. The 

 eoo- or eggs give rise to a number of " poly embryonic" 

 larvae, that ultimately destroy the host. Infected males 

 show in the adult stages many of the characteristics ot 

 the female, the degree to which the change takes plan 

 being mainlv dependent on the stage at which parasitism 



