296 H. M. KINGERY 



not part of the developmental history of these definitive ova. 

 This agrees with the results Duesberg ('08) reports for the sperma- 

 togenesis in the rat; he finds no indication of synapsis. I might 

 say here that the early part of the development of the definitive 

 oocytes in the mouse bears a noticeable resemblance to the growth 

 period of the spermatocytes in the rat, according to Duesberg 

 ('08). Compare his figures 4 to 14 with my figures 28 to 40. 



It is evident, then, that there is no general agreement as to 

 the facts of synizesis and synapsis, that is, whether there is or 

 is not a union, side by side or end to end, of chromatin threads 

 during or after a period when the chromatin is more or less con- 

 tracted in the nucleus. Naturally, then, the interpretations 

 placed on these phenomena do not agree. Three views may be 

 mentioned and briefly discussed here. 



The first is the one held, perhaps, by most workers at present. 

 This is that, during synapsis in oocyte or spermatocyte, chromo- 

 somes of maternal and paternal origin unite side by side, and that 

 there may occur an interchange of materials during the more or 

 less complete fusion. In one of the maturation divisions fol- 

 lowing, maternal chromosomes are separated from paternal; 

 thus, since whole chromosomes pass into daughter cells, a reduc- 

 tion in the number of chromosomes is brought about. This is the 

 view of those who hold what have been termed 'ultimate particle' 

 theories of development and inheritance, based on Weismann's 

 theories and the hypothesis of the individuality of the chromo- 

 somes. These bodies are made up of elements or particles — - 

 'factors' (which may be ultramicroscopic) — linearly arranged, 

 and derived from each parent. These 'factors' are the 'de- 

 terminers' of the characters ('unit characters') in the new in- 

 dividual. During synapsis, when maternal chromosomes con- 

 jugate with paternal, and later, when these chromosomes separate, 

 there is a segregation and redistribution of these 'factors,' so 

 the mature ovum or each spermatozoon has a set of 'factors' 

 differing from those of oocyte or spermatocyte, the character of 

 which has been determined in all probability by chance. The 

 characters of the new individual are determined by the factors 

 brought in by each germ cell in fertilization. Those who hold 



