406 A. J. GOLDFARB. 



The discussion of the results and a more complete bibliography 

 are given in Part III. 



SUMMARY. 



The variation in size of the eggs, the per cent, with jelly layers, 

 the rate of membrane formation and the total cleavage were 

 ascertained for large numbers of freshly liberated eggs from 

 freshly collected females, examined at different periods of the 

 breeding season. 



Three species of sea urchins were studied in this way, namely, 

 Toxopneustes and Hipponoe of tropical waters, and Arbacia of the 

 North Atlantic. 



Large variations from the norm were observed and measured 

 in all four categories. These variations were interpreted as 

 indices of the physiologic condition of the eggs of each female 

 at the time of liberation. 



With the physiologic condition of freshly liberated eggs of a 

 given female known, experiments were then instituted to ascer- 

 tain the nature and extent of the changes in the germ cells, as 

 they aged, or became overripe, under given optimum laboratory 

 conditions. 



The following is a brief statement of the changes in such aging 

 germ cells, viz., changes in size, jelly layer, membrane formation 



and cleavage. 



Change in Size. 



Freshly liberated eggs in good physiologic condition varied but 

 slightly from the norm. For details see text. 



As these eggs aged, their volume increased continuously, until 

 they cytolized or fragmented, and became smaller than the norm. 



Freshly liberated eggs in poor physiologic condition either en- 

 larged but little with age, or were directly reduced in size by 

 cytolysis or fragmentation. 



The nature, extent, and rate of change in size, depends upon 

 the physiologic condition of the eggs when freshly liberated. 

 Whatever the physiologic condition of the eggs may be, their 

 senescence or physiologic deterioration can be very accurately 

 measured by the degree of enlargement or reduction in their size. 



Essentially the same results were obtained in the other two 

 species. 



