304 J- T - PATTERSON. 



explanation of the origin of the asexual larvae, but there are cer- 

 tain obstacles which stand in the way of its full acceptance. In 

 the first place, it is difficult to conceive of any mechanism in the 

 complex polygerm by which predestined germ cells could be 

 nicely and exactly distributed to each of the several hundred 

 sexual embryos which develop from the eggs of Litomastix and 

 Paracopidosomopsis. In the second place, it is a well-known 

 fact that in insects secondary sexual characters and also certain 

 primary sexual characters, such as the organs of copulation and 

 oviposition, are not dependent upon the presence of the gonads 

 for their development. This conclusion is based upon trust- 

 worthy evidences obtained from castration experiments on young 

 larval stages. Furthermore, in the light of modern genetic 

 evidence, I should be inclined to believe that the asexual larvse 

 are sexless not because they have failed to inherit predestined 

 germ cells, but because of their failure to inherit X chromosomes. 

 If X-free blastomeres are formed during cleavage, such cells 

 might become the progenitors of sexless larvse, which in a way 

 could be compared to the non-viable, OY zygote of Drosophila. 



VI. DATA ON SEXES OF OTHER POLYEMBRYONIC INSECTS. 



With the exception of Copidosoma gelechicz and Paracopido- 

 somopsis, exact data on the sexes of polyembryonic insects are 

 very few. The first observations recorded are those of Bugnion 

 ('91), who studied twenty-one cases of Ageniaspis (Encyrtus) 

 fuscicollis and found the following conditions: nine pure female 

 broods; five pure male broods; three broods with males and 

 females in about equal numbers; three broods with large majority 

 of males; one brood with large majority of females. In com- 

 menting upon these data, Marchal ('04) points out that it is 

 difficult to explain the four cases in which the large majority of 

 individuals belong to one or the other sex. He believes, how- 

 ever, that such broods arise from two or more eggs. He further 

 believes that should two eggs, one fertilized and the other not, 

 be laid in the egg at slightly different times, the one deposited 

 first might gain the upper hand in the matter of food, and thus 

 prevent all but a few of the individuals arising from the second 

 egg from reaching maturity. 



