Effects of Castration m Insects 425 



do not destroy the queen of their host colony (Tetramorium ces- 

 pitum), but since the workers of this colony prefer to rear the small 

 sexual forms of the parasites instead of their own bulky males 

 and females, the development of future colonies of the host 

 species is rendered impo ssible and we have here again a case of 

 prospective social castration. 



The conclusion which we reach after marshaling this long 

 series of illustrations of the various forms of castration is that 

 among insects the only case in which destruction or inhibition of 

 the reproductive function clearly results in any modifications of 

 the secondary sexual characters comparable to the modifications 

 observed in vertebrates under like conditions, is that of the sty- 

 lopized andrenine bees as described by Perez. In all the other 

 cases extirpation of or injury to the gonads may indeed result in 

 modifications of the somatic or secondary sexual characters, but 

 the latter do not take on the peculiarities of the opposite sex. 

 The most striking illustrations of the truth of this statement are 

 the insects that have been surgically castrated. These show that 

 the secondar) sexual characters must be so independently and so 

 immovably predetermined and at so early a period in the onto- 

 geny that complete extirpation of the gonads during prepupal 

 life fails to produce the slightest curtailment or modification 

 either in the secondary sexual characters or in the sexual instincts 

 of the adult insect. This conclusion renders it imperative to rein- 

 vestigate the cases of stylopization in the andrenine bees for the 

 purpose of ascertaining whether Perez's interpretation is the only 

 one which they will yield, especially since it has been shown in 

 the first part of this paper that the study of stylopization in 

 Polistes leads to a very different view and one in complete harmony 

 with the other cases of castration in insects. 



It is interesting to note that castrated Crustacea, to judge from 

 the observations of Giard, Geoffrey Smith, and Potts, show modi- 

 fications like those of castrated vertebrates and not like those of 

 the insects. This is in all probability due to the fact that the devel- 

 opment of the primary and secondary sexual characters is grad- 

 ual and continuous in the Crustacea and vertebrates, whereas 

 both these characters in insects are arrested in their develop- 



