3io 



D. H. TENNENT. 



Inasmuch as the basis of my interpretation lies in facts ob- 

 served during the study of the male germ cells, I shall first pre- 

 sent a brief account of these observations. 



The Spermatogenesis of Asterias vulgaris. 



In well-preserved stronger Flemming material stained in iron- 

 haematoxylin the spermatogonia show 18 chromosomes, these 

 all having a slightly constricted or dumb-bell form (Fig. i). The 

 chromosomes are either straight or slightly bent. 



The chromosomes of the primary spermatocytes are nine in 

 number and have at first a distinct dumb-bell form. A precocious 

 longitudinal splitting soon gives them a V or looped form which 

 may be seen in horizontal sections of the equatorial plate (Fig. 2). 



Fig. 

 Fig. 

 Fig. 

 Fig. 

 Fig. 



23 4 



Equatorial plate of spermatogonial mitosis. 

 Spermatocyte of the 1st order. 

 Spermatocyte of the 2d order. Polar view. 

 Spermatocyte of the 2d order. Metaphase. 

 Second spermatocyte division. 



The secondary spermatocytes contain nine chromosomes (Figs. 

 3 and 4). In the second maturation mitosis these appear to be 

 divided transversely (Fig. 5), giving nine as the reduced germ-cell 

 number. 



Studies on Eggs. 



After noting the difference in the somatic number of chro- 

 mosomes in the different lots of eggs sectioned, it became evident 

 that it was desirable to have a set of material in which the eggs 

 from one individual had been treated in three different ways, 

 namely, one set fertilized with sperm, another set treated with 

 C0 2 and a third set treated with C0 2 and subsequently fertilized. 

 I succeeded in obtaining one lot of material of this nature. I 

 shall record my observations in the order of the above statement. 



(«) Observations on Fertilized Eggs. 

 In a successful preparation, the section being sufficiently thick 

 to show the greater number of the chromosomes of the equa- 



