312 PHILLIPS—A REVIEW OF PARTHENOGENESIS.  [Oct. 16, 
cases males are exceedingly rare at all'times or except at certain 
seasons, and it is manifestly to the advantage of the species if it is 
able to survive without the presence of any but propagating 
individuals. ‘Thus in the case of the bee, previously mentioned, it 
would be detrimental to the species to have countless drones feed- 
ing on the hive supplies during the winter; but for the purpose of 
increasing the hereditary influence, it is beneficial to the race to 
feed these males for a brief period when food is plentiful, in order 
that the fertilization may bring about the results known to come in 
all cases from such a union. 
In still other cases the very habits of the animal make the chance 
of the occurrence of a sexual union too small, and in consequence 
the females have acquired the agamic methods of reproduction. 
The case of Cercaria offers a good example of this. If we accept 
the conclusions of Thomas, we see that here we get a transition 
from unisexual to asexual reproduction; and. while these two 
processes are usually widely separated, yet the same difficulty of 
a sexual union may be looked upon as the probable cause of either 
phenomenon. 
Determination of Sex.—From what has gone before we see that 
the problem of sex determination is very closely related to that of 
parthenogenesis, since parthenogenetic eggs so frequently show such 
peculiar sex relations. In some groups unfertilized eggs produce 
only males (arrenotoky), in others only females (thelytoky), while 
in some both sexes are produced (amphoterotoky). ‘Taking as an 
example the Honey Bee, we know that the male eggs are not fertil- 
ized and the female eggs are ; and reasoning from this, it seems true 
that the act of fertilization is the one determining factor, since no 
one has yet been able to find any other fundamental point of 
difference. As was shown under another heading, other explana- 
tions, such as differences in food or size of cell, have been advanced, 
but these have already been answered. Such work as that of Mrs. 
Treat (1873) on Caterpillars, of Born (1881) and Yung (1881) on 
Amphibia, and of Nussbaum (1897) on Rotifers would seem to 
indicate that lack of nourishment favors the production of males; 
but until we have more evidence we are perfectly justified in 
explaining these cases as simply survivals of the more fit sex under 
trying conditions, and cannot use them as arguing for theories like 
those of Dickel. In fact Cuénot (1899) did not succeed in verify- 
ing the results of Mrs. Treat, for he found that the proportions of 
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