
No. 458.] PARTHENOGENESIS. 69 
that these animals are very rare, make its study exceedingly dif- 
ficult. We know no more now than was contained in the work 
of Metschnikoff on Cecidomyia, the account of which appeared 
in 1865, when the maturation divisions of the egg were still 
unknown. Should further research show that pzdogenesis is — 
also introduced by a process of maturation in the egg, it must 
then be regarded as a case of larval parthenogenesis. If, on 
the contrary, the maturation process is wanting in paedogenetic 
development, it would be more reasonable to place paedogenesis 
in the same group with budding. In any event it is a problem 
by itself. 
The process of maturation in the egg is without doubt equally 
indispensable for parthenogenetic development and for that 
resulting from fertilization; yet there is a great difference 
between the two, the importance of which was at once recog- 
nized by Weismann, its discoverer, many years ago. All eggs 
requiring for their development fertilization, undergo a double 
maturation division.. This results in the reduction in the num- 
ber of chromosomes by one half. On the other hand, in the 
majority of parthenogenetic eggs — the single exception being 
that of certain insects — there takes place but one maturation 
division, and in consequence, there is no reduction in the num- 
ber of chromosomes. In this way the opportunities for variation 
are much restricted. The exception to this rule is found in 
those insects in which only one sex develops parthenogenetically, 
and in the male individuals in those cases where both sexes de- 
velop parthenogenetically. In such cases two maturation divi 
sions invariably take place with a corresponding reduction in 
the number of chromosomes. The insects which on account of 
the possession of this peculiarity have been much studied lately, 
are the ants and the bees. In these Hymenoptera it is only the 
males that develop parthenogenetically. I have every anon 
to re-affirm this, notwithstanding the recent objection raised 
against it. ; 
After what I have said about fertilization it is clear that 
microscopic study, and that only, is able to show without error 
whether an egg is fertilized or not. The development of an 
aster around the centrosome of the spermatozoön after the lat- 

