I5O . M. W. BLACK MAN. 



In ScoJopendra (Blackman, 105, op. cit.} there are two distinct 

 types of spermatocytes readily divisible on the basis of size. 

 Those characterized by the larger size are about twice the average 

 diameter of the smaller ones and vary from them in behavior in 

 the two maturation divisions. But this variation in behavior 

 concerns the achromatic structures of .the cell and seems to be 

 due to the much greater amount of cytoplasmic and archoplasmic 

 material present in the larger cells. It is extremely interesting 

 to note that as regards the behavior of the chromosomes these 

 two sizes of spermatocytes are essentially identical. Indeed, the 

 chromosome groups of the small cells differ in no respect from 

 those of the large type. The elements are no smaller than in 

 many of the large cells and present the same constancy in form 

 and the same size relations characteristic of the large type of cells. 

 Figs. 1 6, 17, 1 8 represent the chromosome groups of the small 

 type of spermatocytes. Many more were carefully studied and 

 drawn and all show the same characteristic shapes and size rela- 

 tions typical of the spermatocyte chromosomes. In fact, the 

 only reason more of these were not used is that they are not so 

 desirable for study owning to the difficulty in drawing them due 

 to their closer crowding in the metaphase. 



The shape of the daughter chromosomes as they move apart 

 to the poles in the anaphase of the first spermatocyte mitosis is 

 quite characteristically different for the different types of chro- 

 mosomes (Figs. I, II, IV, //, III, i). Those resulting from the 

 division of cross-shaped tetrads have the three lobed appearance 

 shown in Fig. I, //. The daughter chromosomes resulting from 

 the division of the double-V-shaped tetrads have the shape shown 

 in Fig. II, //, and are essentially single-V-shaped chromosomes, 

 as is shown at a later stage. Those resulting from the division 

 of the double-rod tetrads, as they move toward the poles, have 

 the form of single rods, slightly constricted near the middle. I 

 have been unable to identify positively the division products of 

 the tetrad which undergoes its reduction division in the first 

 mitosis, but in several anaphases six of the daughter chromosomes 

 of each group are V-shaped, and it is probable that the sixth one 

 of this shape is the chromosome in question. This is rendered 

 more certain by the observation that in these cells there are but 



