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 

 taniatus 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 



