STUDIES ON CHROMOSOMES 56 



all the stages. The agreement of great numbers of division-fig-- 

 ures from both testes leaves no doubt regarding the constancy of 

 the essential phenomena (with rare minor variations, as indicated 

 beyond). As will be seen, the modification of the diploid groups 

 has led to corresponding modifications of the maturation-process 

 that are most interesting in relation to some of the problems of 

 synapsis and of the qualitative differences of the chromosomes. 



DESCRIPTIVE 

 a. The spermatogonial groups 



The peculiar anomaly of the chromosome groups, first seen in 

 the spermatocyte-divisions, led me to examine the spermatogonial 

 groups with particular care, and it will be worth while to state 

 both the preliminary and the definitive results. These groups 

 are in the nature of the case more difficult than those of the sper- 

 matocytes, owing to the greater number, smaller size, and greater 

 crowding of the chromosomes; hence, only flat metaphase-plates 

 and such as are not very oblique to the plane of section can safety 

 be used. A search through the numerous dividing spermatogonia 

 showed 35 cases that seemed to meet these conditions and also 

 to show no serious obscurity or confusion of the chromosomes. 

 Many of these are of almost schematic clearness, and some are 

 well adapted for photographic reproduction. The first examina- 

 tion showed undoubtedly that 29 of the 35 cases contained 22 

 chromosomes each, including 19 large and three very small ones. 

 Of the six exceptions, three seemed to lack one of the small ones, 

 two, one of the large ones, and one a large and a small. Closer 

 study of these six cases ultimately showed that in four cases 

 the apparently missing third small chromosome was in reality 

 present, though hidden among the larger chromosomes, while in 

 two cases an apparently missing larger chromosome was found 

 lying immediately below another one, the metaphase-plate not 

 yet having become perfectly flat. This leaves but one exception 

 in 35 cases, and we shall hardly go astray in the conclusion that 

 this exception is probably the result of accident. In any case we 

 may confidently conclude that the chromosome-group shown in 



