UROGENITAL SYSTEM. 347 
In the formation and maturation of spermatozoa and eggs a peculiar substance in 
the nucleus—chromatin— becomes aggregated in small bodies called chromosomes, 
the number of which in the mature genital products is half of that occurring in 
the other cells of the body. In most species the number in the body cells is always 
even and is therefore exactly divisible, but it was found that in certain insects there 
were differences between the sexes, the male having an odd, the female an even 
number. When the reduction division occurs, by which the chromosomes are 
divided between the mature eggs or the spermatozoa (for details see cytological 
works), the eggs would all have the same number of chromosomes while the 
spermatozoa would be dimorphic, some having an odd and some an even 
number of chromosomes, In other cases there is frequently one or more 
chromosomes (idiochromosomes) which differ from the rest, and these are dis- 
tributed in the same way at the reduction division. At the fertilization of the 
egg there is an addition of the chromosomes of the spermatozoa to those of the 
egg, consequently some of the eggs will have the odd number and some the 
even number of chromosomes, this being perpetuated in all of the cells of the 
resulting organism until the next reduction division. It would thus follow that 
sex was determined at the time of fertilization of the egg. But this is difficult 
to reconcile with the existence of hermaphroditism. 
Another view, which better accords with the facts, is that sex is a matter of 
Mendelian inheritance, the females in some instances being heterozygous, the 
males homozygous; or these relations may be reversed In the first condition 
the element of ‘femaleness’ dominates over the recessive ‘maleness’, In such 
cases it seems reasonable to suppose that the hermaphrodites are really 
heterozygous females in which the normally recessive ‘maleness’ has become 
equally potent with the female, while under ordinary conditions the matter of 
sex is dependent upon the character of the chromosomes combined with the 
Mendelian inheritance, 
Among the cyclostomes there are occasional specimens of lam- 
preys which have been regarded as hermaphroditic, but in the myx- 
inoids this is the regular occurrence, the anterior end of the gonad 
is male and the posterior female. One or the other of these is func- 
tional, the animal being predominantly either male or female, and 
some individuals are regarded as sterile. Nansen regards this as a 
case of proterandric hermaphroditism. In the teleosts several species, 
of Serranus are regularly hermaphroditic as is Chrysophrys aurata, 
while in several other species it is an occasional occurrence. Triton 
teniatus is the only urodele in which it is reported, but in the anura it 
is more common. ‘Thus it is frequent in the frogs and occasional in 
other genera. In the toads (Bufo) there is frequently a ‘Bidder’s 
organ’ in front of the gonads which contains immature ova in the 
male. Among the birds the phenomenon has been reported in the 
chaffinch. (The assumption of male plumage by female birds at the 
