4o6 William Morton fVheeler 



is required to establish the truth of this statement. The other 

 case is even more doubtful. Silvestri ('06) recently described 

 Copidosoma truncatellum, a chalcidid which is polyembryonic 

 and infests the eggs and caterpillars of moths belonging to the 

 genus Plusia, as possessing two very different larval forms. One 

 of these he designates as "asexual" and states that it lacks every 

 trace of the reproductive organs. It is very unlike the ordinary 

 sexual larva in having a large head, well-developed mandibles and 

 a very slender nematode-hke body, and never lives beyond the 

 larval stage. Silvestri believes that it has been developed for the 

 purpose of breaking down the tissues of the host caterpillar and 

 of thus rendering them more easily assimilable by the sexual larvae 

 which alone develop into imagmes. The following considerations 

 seem to me to cast considerable doubt on this interpretation: 

 First, the asexual larvae figured and described by this investigator 

 are suspiciously like certain very young ichneumonid larvae, and 

 as their development is not satisfactorily traced to the same cell- 

 masses from which the sexual Copidosoma larvae arise, it is not 

 improbable that the two larval forms really belong to two very 

 different parasites. In other words, Silvestri's Plusia caterpillars 

 were probably infested with ichneumonid in addition to Copido- 

 soma larvae. Second, I have been unable to find any larvae of the 

 asexual type in a number of American Plusia gamma caterpillars 

 which were heavily infested with Copidosoma truncatellum. 

 Third, as in many species of Chalcididae larvae of Silvestri's sexual 

 type are able by their own endeavors to break down and assimi- 

 late the tissues of their host, it seems improbable that a single spe- 

 cies should have developed a peculiar sexless and moribund larva 

 for this particular purpose. 



5. Nutricial castration 



The abortive or rudimental condition of the sexual organs 

 seen in the cases of alimentary castration may be normally pro- 

 longed and maintained throughout the adult life oi the workers 

 among the social Hymenoptera, when these insects are compelled 

 to live on the slender remnant of food that remains to them after 



