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." 
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 (’08) states that Crisia geniculata and C. cornuta (or edwardsiana, 
according to her later identification, 710) are probably monoecious. 
