136 .1. T. CUNNINGHAM. 



the centrosome within the germinal vesicle, while there is 

 some, although not complete, evidence of the identity of the 

 vitelline nucleus with the centrosome left at the last division 

 of the germ-cell. The centrosome of the ovum then de- 

 generates and disappears before the two polar divisions, and 

 this suggests the question whether there is anything in the 

 process of spermatogenesis which corresponds to this occur- 

 rence in the ovum. 



It has been found that the reduction divisions of the sper- 

 matocyte take place in the same way as in the ovum — that is 

 to say, before the last two divisions there appear half the 

 proper number of chromosomes, each of which consists of 

 four distinct particles, and after the divisions one of these 

 particles is contained in each spermatozoon. 



According to O. vora Rath there are four generations or 

 divisions of the male germ-cells before the last two, or reduc- 

 tion divisions, which take place by what he terms "heterotypical 

 mitosis,^^ because of its special character. He finds the cell 

 of the fourth generation larger than that of the third, and 

 believes that there is a resting and growing phase after the 

 third generation. But he does not mention any degeneration 

 or disappearance of the centrosome between the fourth division 

 and the first reduction division, and this is the interval where 

 such an occurrence is to be sought. He figures one of the 

 large resting cells of the third generation, and says that often 

 near the resting nucleus at a spot where the cytoplasm has a 

 coarse granular appearance and dark colour, he has seen two 

 round bodies, which he takes to be two attraction spheres 

 with their centrosomes, as they are too large for centrosomes 

 alone. 



According to vom Rath, the tetrads or groups of four chro- 

 matin bodies which are present at the commencement of the 

 reduction divisions in the spermatocyte are formed directly 

 without a resting phase from the dyaster of the previous 

 division. Thus the process does not agree with that which 

 takes place in the ovum. But he points out that in the growth- 

 period of the ovum, according to certain observations, the 



