-7Q2 William Morton Wheeler 



these characters may be so fixed and so nearly independent of the 

 gonads, except, perhaps, in the very earhest larval or late em- 

 bryonic stages, as to remain quite unaffected in their development 

 after the gonads have been completely removed. The degree of 

 this independence may be supposed to differ in different insects 

 and even in different individuals of the same species. It may be 

 sHght or almost absent in Andrena and very well marked in Polis- 

 tes and this may account for the differences between the stylo- 

 pized specimens in the two genera. 



2. The difference in the manifestation of changes in the second- 

 ary sexual characters may, however, be due to ethological differ- 

 ences between the two genera. Andrena has only male and female 

 forms and both under normal conditions are adequately fed in 

 their larval stages. In Polistes the larvae of the earlier broods in 

 the annual series, as Marchal has show^n ('96, '97) are poorly fed 

 and as a result become sterile fem.ales, or workers. As imagines 

 they maintain them.selves in a sterile condition by appropriating 

 very little of the food they collect to their own use, since the)' at 

 once lavish it in feeding the succeeding broods. Hence the females 

 of these earlier broods become sterile, in the first place through 

 alimentary castration of the larvae from which they develop, and 

 in the second place, maintain themselves in this condition as 

 adults through the nursing or nutricial function (nutricial castra- 

 tion). These peculiar phenomena will be more fully discussed in 

 the second part of this paper. Owing to these two forms of physio- 

 logical castration inhibition of the development of the reproduc- 

 tive organs is a common and normal occurrence in Polistes females, 

 and the parasitic castration induced by Xenos would not be ex- 

 pected to produce somatic changes of such magnitude or of 

 such a nature as Perez has observed in Andrena, all the females ot 

 which are normally fertile mothers. In other words, the effects of 

 the Xenos on their hosts is of the same nature as the ahmentary 

 castration to which all the earlier broods during the seasonal 

 development of the Polistes colony are normally subjected, and 

 this probably accounts for the absence of any specific effects on 

 stature and structure and the evident ease with which the volu- 

 minous parasites are borne and tolerated. 



