40 THOS. H. MONTGOMERY jr., 



C. The spermatocytic mitoses. 



a) The prophases. 



In the resting 1st spermatocytes (Figs. 95—100), as has been 

 shown, separate chromosomes cannot be distinguished. The commence- 

 ment of the prophase of the first mitosis is marked by a change 

 in the arrangement of the chromatin (PL 3, Figs. 100 — 104). The 

 chromatin reticulum gradually separates out into separate strands, 

 i. e. there is a retraction of its anastomosing processes. Simultaneously 

 the structure of the strands becomes denser : now the chromatin 

 microsomes become grouped close together, while in the preceding 

 rest stage the chromatin was loosely granular or even fibrillar in 

 appearence. While this process is taking place, the reticulum has 

 broken up into a number of loops (chromosomes), which vary in 

 diameter and length, and all of which have at first irregular surfaces 

 (Figs. 104, 105); but there is no monilation of these loops as was 

 found in the telophase. 



At it is of great importance to determine the number of these 

 chromosomes, I have counted them with care in a number of nuclei, 

 and only in those cases where the whole nucleus lay in the plane of 

 the section. The loops were counted, by carefully drawing them, in 

 13 nuclei (Figs. 105—112, 114—118): of this number, 4 contained 

 3 loops each; 5 contained 4 loops each; 2 contained 5 loops each; 

 1 contained 6 loops; and 1 (Fig. Ill) contained either 3 or 4, I could 

 not determine which. Thus we find that the number varies from 

 3 to 6 in different nuclei, 3 or 4 being most frequently found. No 

 nucleus was found with only a single loop. Thus in the early prophase, 

 which represents the ''dense spirem" stage of other objects, a single 

 continuous chromatin thread does not occur: that is, the spirem stage 

 of the spermatocytes, unlike that of the spermatogonia, shows from 

 the first a number of separate loops. In my preliminary paper ('97) 

 on this subject I stated that a single continuous thread was produced ; 

 this erroneous conclusion was due to the observation of a nucleus 

 which did not lie wholly in the plane of the section , with the con- 

 sequence that all of its loops could not be seen. I have paid particular 

 attention to this matter of the singleness or multiplicity of the chro- 

 matin loops, and to their exact number, and am convinced that a 

 continuous spirem does not occur at any period in the prophase, since 

 I have never found a nucleus with less than 3 loops. 



We found that in the postsynapsis and telophase preceding the 

 rest stage, the number of chromosomes to a nucleus varied from 3 



