436 



FERXANDUS PAYNE. 



eggs form a single layer with small cells wedged in between. In 

 the testes there are many cells showing all stages of development 

 from the spermatogonia to the mature sperm. The first polar 

 spindle is formed before the eggs leave the ovary, but I have 

 never found the division completed. In material from Boss 

 Lake the late anaphase has been seen in a few instances (Payne, 

 '24), but many eggs, in material from Boss Lake and also from 

 Kentucky, show the first polar spindle in metaphase or slightly 

 earlier. 



The first cleavage is equal, but after this inequalities enter 

 (Figs, i, 2, and 3). The rate of cleavage becomes unequal from 

 the two-cell stage. Figure I shows a three-cell stage. Even at 



FIGS. 5 AND 6. 5 shows the method of endoderm formation; 6 the solid 

 endoderm. 



this time a large cavity is present between the blastomeres. 

 Continued cleavage results in the production of a blastula, the 

 cells of which are long, pointed at the inner ends, and larger at 

 the peripheral ends. The cavity of the blastula is small (Fig. 4). 

 The yolk has accumulated near the inner ends of the cells, so 

 that even in the living blastula the outer ends look clear while 

 the inner ends are opaque. The nucleus lies in the outer clear 

 end. The larva is ciliated and swims about freely at this stage. 

 At what stage the cilia disappear I am not sure, but it occurs 

 before elongation begins. 



The method of endoderm formation is similar to, but shows 

 some variations from the process in other Hydromedusae. There 

 is a slight invagination at one side, probably the vegetal pole. 1 



1 I shall use the terms "vegetal" and "animal" pole to describe the differences 

 observed rather than to indicate a distinct polarity. I have not oriented the egg 

 t make sure that endoderm formation occurs at the vegetal pole. 



