2 ir. L. WIEMAN 



niid otluM in:it(M iai 1 am greatly indebted to Di'. I*aiil(i. Woolley 

 Director of i\\c Palholoj^ic Institute of tlic Cincinnati (lonora,! 

 Hospital, to whom my thanks are d\w. 



The material was fixed in a modification of Jiouin's solution 

 (similar to Allen's B-15, used with and without chromic acid 

 and ui(>a) with excellent results. Sections were cut 7 micra 

 in thickiu^ss and stained in two w^ays, namely, Schwaardemaker's 

 safr-anin and IJchtgriin, and iron alum haematoxylin. These 

 two methods are excellent checks on each other. Of the two 

 probably safranin-lichtgriin is the more valuable for counting 

 chromosomes and for differentiating betw^een chromosomes and 

 plasmosomes. 



I. OBSERVATIONS 



The most favorable period in the germ cycle in w^hich to 

 study the chromosomes proved to be the dividing stages of 

 primary spermatocytes and for this reason considerable atten- 

 tion was devoted to this stage. As in most mammalian material 

 the two principal difhculties in a study of this kind are, first, 

 the fact that only rarely is a metaphase plate formed in which 

 all of the chromosomes lie in one plane, and second, a tendency 

 for the chromosomes to adhere in clumps. Generally the 

 chromosomes begin dividing before an equatorial plate stage is 

 reached and one must be very careful in making counts not to 

 omit chromosomes lying above or below^ the main group. Side 

 and oblique view^s and, best of all, early anaphase stages are 

 valuable in checking up polar-view observations. In cases 

 selected for careful study only cells whose chromosome groups 

 were entirely included in the thickness of the section were used, 

 except as noted below. 



Figures 11, 12, 13, 14, 15 and 16 are drawings of primary 

 spermatocyte chromosomes at what is approximately the meta- 

 phase stage of division. In figures 11, 12, 15 and 16 no division 

 has occurred, and 12 obviously bivalent chromosomes may be 

 counted. In figures 13 and 14 one chromosome in each group 

 has divided and the products of this division are marked r/i 

 and 02. All of these drawings were made from white material. 



