644 J. T. PATTERSON 



' It might be argued that the identity of sex among the several 

 individuals of a polyembryonic litter is the result of similarity of 

 environment. But here again the facts of fertilization in the 

 development of Litomastix completely disproves the idea that 

 external influences are in any way causal factors in sex deter- 

 mination, at least in this parasitic insect. Furthermore, in the 

 case of the development of the armadillo the four embryonic 

 primordia early become separated from each other, each embryo 

 becoming enclosed within its own amniotic envelope, and in a 

 great measure acquiring its own individual environment. All of 

 this takes place long before the sexual organs develop, indeed, 

 long before the so-called ' hermaphroditic stage' of the embryo 

 appears. If external factors play any role in sex determination, 

 it is difficult to understand, under the conditions obtaining in the 

 armadillo, why litters containing both male and female individ- 

 uals are never produced. 



The study of polyembryonic development in Litomastix also 

 calls to mind another important fact, viz., that polyembryony 

 has nothing to do with the actual determination of the sex of the 

 egg. This conclusion becomes evident if one considers the differ- 

 ent sexual conditions which exist in the several species exhibit- 

 ing polyembryony. It occurs in the typical dioecious species, 

 like the armadillo, in which the fertilized egg produces all females 

 or all males, it occurs in the parasitic hymenoptera, in which the 

 fertilized egg produces females, and the unfertilized egg males; 

 and finally, it occurs in hermaphroditic forms, like the earth 

 worm, and also (probably) certain cyclostomatous Bryozoa. 16 



Polyembryonic development may obtain, therefore, no matter 

 whether the egg be fertilized or not, or whether it is destined to 

 bring forth a progeny of unisexual or one of bisexual individuals. 

 Let us repeat, then, that polyembryonic development is not to be 

 considered as a causal factor in sex determination. The facts 

 of polyembryonic development adds, rather strong corrobora- 

 tive evidence to that of cytology, namely, that the sex poten- 

 tiality of the egg is fixed at a very early stage of development 

 doubtless in all ordinary cases, at the time of fertilization. 



16 Robertson ('03) states that Crisia geniculata and C. cornuta (or edwardsiana, 

 according to her later identification, '10) are probably monoecious. 



