SEGREGATION OF HOMOLOGOUS CHROMOSOMES 447 



at least, in one of the short-horned grasshoppers, Phrynotettix 

 magnus, by Wenrich ('16) who, through years of close study, 

 has been able to follow one well marked individual chromosome 

 pair from the spermatogonia through the most diffuse stages to 

 the spermatids. The other one-time hypothesis of Van Beneden 

 ('83) that one-half of the chromosomes are of paternal and one- 

 half of maternal origin was clearly shown to be a fact by the 

 late CarlMulsow ('12) in his study of the gametogenesis and 

 fertilization of a parasitic trematode, Ancyracanthus, in which 

 the chromosomes may be counted, even in the living spermato- 

 zoon as it enters the egg and fuses with the female pronucleus. 



Sutton ('02) was the first to furnish actual support for the 

 latter hypothesis and to suggest a thorough-going correlation of 

 the chromosomes and somatic characters; he recognized in 

 Brachystola magna a double series of chromosomes in the sper- 

 matogonia which he considered to be of biparental origin. He 

 indicated the probable relationship between Mendelian phe- 

 nomena and the possible distribution of the chromosomes in the 

 gametes and their recombination in the zygote. But, so long- 

 as the homologous chromosomes of this double series were indis- 

 tinguishable, it was impossible to follow, cytologically, the chro- 

 mosomes derived from a given parent and to determine their 

 manner of segregation in relation to any other chromosomes. 



As is well known, in the Orthoptera and many other animals 

 as well, the first maturation division determines which of the 

 derivative cells will, in fertilization, produce a male and which 

 a female, since the accessory chromosome — the sex determinant 

 — passes undivided into one of the daughter cells at this time. 

 While probably it is purely a matter of chance which of the 

 daughter cells the accessory enters — that is, it parallels any 

 Mendelian character in the matter of segregation — nevertheless, 

 it marks unalterably, after it has passed to one pole, the male 

 from the female producing spermatozoon. If one of the homo- 

 logues of any pair is recognizably different from its mate and 

 these homologues should segregate from each other at the first 

 maturation division their manner of segregation in relation to 

 sex would be apparent. The only instances of this sort to be 



