314 J. E. WODSEDALEK. 



PLATE IV. 



FIGS. 28 AXD 29. Cells showing the formation of the secondary spermatocytes 

 from the primary spermatocyte division. The eighteen chromosomes pair loosely 

 to form nine bivalents which are present in the one type of secondary spermatocyte 

 and in the other type are shown the nine bivalents and the sex-chromosome. 



FIG. 30. Metaphase stage of division of the one type of secondary spermatocyte 

 showing the nine bivalent chromosomes and the sex-chromosome. 



FIG. 31. Metaphase stage of division of the other type of secondary spermato- 

 cyte showing only the nine bivalent chromosomes. 



FIGS. 32-34. Division stages of the secondary spermatocyte with the sex- 

 chromosome showing the division of all of the chromosomes, including the sex- 

 element, giving rise to spermatids both of which contain the sex-chromosome. 

 When the division of the cell is complete (Fig. 34) each of the nine ordinary chromo- 

 some splits into two so that in reality there are eighteen ordinary chromosomes plus 

 the sex-chromosome in this type of spermatid. 



FIGS. 35-37. Division stages of the secondary spermatocyte without the sex- 

 chromosome. Figure 37 shows the splitting up of the nine chromosomes at the 

 poles so that there are in reality eighteen chromosomes passed on to the other type 

 of spermatid. 



FIG. 38. A newly formed spermatid showing the eighteen chromosomes. 



FIG. 39. A mature spermatozoan of the smaller type undoubtedly without the 

 sex-chromosome. 



FIG. 40. A mature spermatozoan of the larger type which undoubtedly contains 

 the sex-chromosome. 



