EXPLANATION OF PLATES 



All figures are table level drawings outlined with the camera lucida at the 

 niagnifieation produced by 1.5 mm. Zeiss objective and 18 compensating ocular. 

 Details were drawn in with the same objective and 12 compensating ocular. 

 The monobjective binocular microscope was found to be very useful in verifying 

 the findings of the ordinary compound microscope. Owing to differences in 

 angle from which the chromosomes were drawn, there is some variation in size 

 of individual chromosomes in different figures. The figures have been repro- 

 duced I off. 



ABBREVIATIONS 



^ , Y , the members of a pair of unequal m, small liivalent chromosome. 



idiochrosomes. 

 X, y, the members of bipartite chroma- p, the plasmosome of the primary sper- 



tin nucleolus of the growth period matocyte. 



of the first spermatocyte, and also of 



the interkinesis nucleus. 



Other abbreviations explained below. 



PLATE 1 



EXPLANATIOX OF FIGURES 



1 Spermatogonium, late ])rophase, white, showing 24 chromosomes. 



2 Spermatogonium, late prophase, negro, showing 24 chromosomes. 



The difference in size in the two figures is, I believe, without special signifi- 

 cance. Figure 1 is from a Safranin-Lichtgrun preparation and figure 2 from an 

 iron-alum-haematoxylin slide. The latter is reconstructed from two adjacent 

 sections. 



3 Large abnormal spermatogonial metaphase, white, showing approximately 

 48 chromosomes. 



4 Examples of various types of chromosome nucleolus. 



5 and 6 Primary spermatocyte, growth period, white. 



7 Primary spermatocyte, nucleus, growth period, negro. 



14 



