200 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



its development until the following season ; that is, it becomes a "winter 

 egg." From such eggs there hatch invariably agamic females. 



These facts support the view already advanced, that in parthenogenetic 

 animals a segregation of sex-characters takes place at the formation of the 

 second polar cell. The female character passes into the second polar cell, 

 leaving only the male character in the egg. Hence, if the egg which has 

 formed two polar cells develops without fertilization, it must develop into 

 a male. But if such an egg is fertilized, it invariably forms a parthenoge- 

 netic female, 9 {$), that is, an individual in which the male character is 

 recessive. Accordingly the functional spermatozoon must in such cases 

 invariably bear the female character, and this is as invariably dominant 

 over the male character when the two meet in fertilization. 



But we are now confronted with a serious difficulty. The egg, which 

 has formed two polar cells, we have supposed, is purely male, yet the 

 animal which develops from it by parthenogenesis produces only gametes 

 purely female. 



The studies of Petrunkewitsch (:0l) on tlie iioney-bee give us a clue 

 to the solution of this difficulty. The genital gland of the male bee 

 probably develops, not from any part of the mature egg, but from the 

 second polar cell, after the union of that body with one of the two prod- 

 ucts of division of the first polar cell. But the second polar cell con- 

 tains, according to our hypothesis, only the female character ; the same 

 is probably true of one of the products of division of the first polar cell, 

 perhaps of that one which fuses with the second polar cell. If so, the 

 genital gland of the male bee will contain onli/ the female character, and 

 in the spermatogenesis of the bee, no segregation of sex-characters will 

 be found to occur. On the other hand, if the male character is borne by 

 that derivative of the first polar cell which fuses with the second polar 

 cell, the body formed by their union will contain both the male and 

 female characters, and will be homologous with the cleavage nucleus of 

 a fertilized e^Q. In that case we shall expect to find the occurrence of 

 a normal process of spermatogenesis with segregation of sex-characters. 

 If this is so, there doubtless are produced male as well as female sper- 

 matozoa in the honey-bee, but the latter sort alone can be functional 

 because the fecundable egg, as we have seen^ invai'iably bears the male 

 character. 



In support of the important observation of Petrunkewitsch may be 

 cited the earlier observation of Henking ('93). Ho finds that, as a rule, 

 in insects generally no polar cells arc formed at maturation, but merely 

 polar nuclei which remain imbedded in the cytoplasm of the egg. The 



