629 



349 110 45 



In degeneration 8, total 512. 



in one section, not to mention the fact of there being two "germinal 

 ridges", it is sometimes a difficult matter to decide whether a cer- 

 tain cell is a new appearance, or only a portion of a cell present in 

 a preceding section. 



There was not the shadow of an idea in my mind how many 

 germ-cells the embryo contained, before the counting began. Neither 

 was there any thought of bringing this number into genetic relation- 

 ships with one or two original cells of the egg-cleavage. It was only 

 when the total came to a little over 500 that a natural suspicion of 

 this arose. 



Among the results of Rückert's recent and brilliant work ('99) 

 is the discovery, that in certain Elasmobranchs the cleavage-products 

 divide synchronously at least 10 times. Now, as will subsequently 

 appear, there is ample reason for deriving the germ-cells of Raja 

 bails from some period of the egg-cleavage. Moreover, from their 

 close similarity in size, not only throughout individual embryos, like 



