POLYEMBRYONIC DEVELOPMENT IN TATUSIA 643 
ical juggling of blastomeres to account for the various relation- 
ships and positions assumed between the components of these 
monsters. 
4. Polyembryony and sex 
One of the obvious biological bearings that the study of poly- 
embryonic development has revealed concerns heredity, includ- 
ing the heredity of sex. The illuminating studies of McClung 
(03), Stevens (06), Wilson (’05-’12), Morgan (’09) and many 
others, including the recent excellent paper on Ancyracanthus by 
Mulsow (’12), have shown that in a large number of animal forms 
' the heredity of sex is in some way bound up with certain co-called 
sex chomosomes, and that, as a consequence, the sex of a given 
individual is irrevocably fixed at the time of fertilization, or in the 
case of an unfertilized or parthenogenetic egg, not later than the 
time the egg starts to develop. 
It is in this connection that polyembryonic development fur- 
nishes a very strong confirmation of the modern cytological view 
of sex heredity. For in every authenic case of polyembryony 
among dioecious species all of the individuals arising from one 
egg are invariably of the same sex; that is they are either all males 
or all females, never mixed. The most logical conclusion that 
can be drawn from these facts is that the sex character is stamped 
upon the egg prior to the origin of the several individuals to which. 
it gives rise. ‘That the sex of the egg is determined as early as 
the time at which development begins, seems certain in the case 
of parasitic hymenoptera. It will be recalled that Silvestri (06) 
has shown in Litomastix (and he thinks that is is almost cer- 
tainly true in Ageniaspis) that the fertilized egg produces females 
only, while the unfertilized egg gives rise to males only, exactly 
as in the well known case of the bee. Here fertilization or the 
lack thereof determines the sex of the offspring, and, no matter 
how many individuals the egg may produce by polyembryonic 
development—and in Litomastix the astonishingly large number 
of about 3000 may develop—they are all of the same sex." 
15 Hxcept, of course, the so-called asexual larvae —the origin and development 
of each needs further study. 
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