216 Basis of Sex Determination 



period of rest lasts. If the larvae are allowed to settle 

 on the proboscis of the adult female but are removed 

 too early hermaphrodites are produced having male and 

 female characters mixed. 



Baltzer has suggested on the basis of some observa- 

 tions that the larvae while on the proboscis of the female 

 absorb some substance secreted by the proboscis, and 

 this substance accelerates the further development 

 into a male and suppresses the female tendency. If 

 this substance from the proboscis does not reach the 

 larvae the tendency to become males is gradually 

 suppressed in the majority and only a few develop into 

 pure males or protandric hermaphrodites, while the 

 female characters are given a chance to develop. 

 Baltzer assumes, therefore, as it seems to us correctly 

 that in all larvae the tendency for both sexual char- 

 acters is present, that they are, in other words, herma- 

 phrodites, but the chance for the suppression of one 

 and the development of the other group of characters 

 can be influenced by certain chemical substances which 

 the larva may take up. x 



Giard has studied the effects of a curious form of cas- 

 tration brought about by parasites, which is followed 

 by a change in the sexual character of the castrated 

 animal. The phenomenon is very striking in certain 

 forms of crabs when they are attacked by a parasitic 

 crustacean, Sacculina. The two sexes differ in the crab 



1 Baltzer, P., Mitteil. d. zoolog. Station, Neapel, 1914, xxii. 



