568 FERNANDUS PAYNE 



than in any of the others. Shortly after the last spermatogonial 

 division and throughout the entire growth period, two and some- 

 times three chromatin nucleoli are present in the nucleus. In the 

 prophases of the first spermatocyte division only one large 

 nucleolus remains. Whether the second and third one disap- 

 pear or whether all of them fuse, I cannot say. Stevens ('10) 

 describes the second and third bodies as plasmosomes, but with 

 hemotoxylin all of them stain alike. At any rate, from the 

 single nucleolus there arises in late prophases the unequal pair 

 of chromosomes. This is shown particularly well in figure 1, /. 

 Most of the time a third small body is either in contact with them 

 or lying very close (fig. 1, F, G, H, I). What this small body 

 is I do not know, but believe it is not a chromosome as it is 

 smaller than any of those which appear in the first spermatocytes. 

 It persists until the late prophases (fig. 1, K) and then can be 

 traced no further. It will be noticed in figure 1, /, that the size 

 difference between the components of the unequal pair is greater 

 during the early prophases than in metaphase. 



Zweiger explains these irregularities in number by assuming 

 that in cells with 12 chromosomes no accessory is present; in cells 

 with 13, one accessory is present and in cells with 14, two ac- 

 cessory chromosomes are present. He further assumes that the 

 accessory chromosomes divide in both maturation divisions, 

 something which no accessory chromosome has ever been ob- 

 served to do. I am using the word 'accessory' in the sense that 

 it has been used by various authors in the recent work on chro- 

 mosomes which are related to sex. It is a spermatogonial chro- 

 mosome which has no mate with which to pair at synapsis and 

 which appears in the spermatocyte divisions as a univalent chro- 

 mosome and hence divides in only one of them. The spermato- 

 zoon which receives this chromosome is female producing and the 

 other is male producing. It is readily seen that Zweiger's 

 'accessorisches Chromosom' is not of this type. He describes 

 his 13 chromosome group as containing one accessory chromosome 

 and assumes that such groups arise from spermatogonial cells 

 with 26 chromosomes. Hence all 13 would be bivalent. My 

 observations show clearly that when 13 chromosomes are present, 



