356 



J. T. PATTERSON. 



the nine complete lots (Broods 2 to 10) listed in Table V., the 

 number of females in each case is greater than the number of 

 males. In some cases (Broods 3, 4, 5, 7, 8), this difference is not 

 so great but that the origin of each lot can be explained on the 

 assumption that two eggs have been deposited in the egg of the 

 host. But in Broods 2, 6, 9, and 10 the number of females in 

 excess of males is indeed striking, making it difficult to explain 

 the origin of such broods on the basis of two eggs. 



In view of these facts, the writer is convinced that some other 

 explanation must be offered for the origin of certain mixed broods; 

 in fact, one involving the idea that a single fertilized egg may give 

 rise to a few males as well as a relatively large number of females. 

 This would be possible on the basis of the following assumption. 



TABLE V. 



TABLE SHOWING THE NUMBER OF PARASITES IN MIXED BROODS. 



* This brood is not complete, owing to the fact that some of the larvae and pupae 

 had been destroyed by a large dipterous larva. 



If Copidosoma conforms to the general scheme for sex determin- 

 ation in insects, the females must have the 2 X chromosomes, and 

 males the single X chromosome. Ordinarily, during the process 

 of cleavage, all of the chromosomes in the fertilized egg divide 

 equally, so that all of the nuclei entering into the formation of 

 the embryos will carry the XX chromosomes, thus producing a 

 brood of females. But if during the early development of the 

 egg it should happen that the two X chromosomes in one or more 

 cleavages should not divide but separate, one going to each pole 

 of the spindle, each daughter nucleus would then receive a single 



