468 



figures. Indeed, it would be uo exaggeration to say, that almost all 

 the drawings show them ; for it is only very late in the development, 

 that activity sets in among the primary germ-cells, and their number 

 becomes increased. 



Balfour ('78, 2) distinguishes between "primitive ova" and 

 "permanent ova". My researches amply confirm him, but for obvious 

 reasons the former name must give place to primary germ-cells, the 

 latter to secondary ones. In Raja batis the primary germ-cells persist 

 as such, until the embryo is at least 42 mm, secondary germ-cells 

 are those of older embryos, from my investigations those of embryos 

 of 54 mm onwards. 



Primary germ-cells from early embryos, normal both in position 

 and general characters, are those of plate 1. The usual size of such 

 is 0,02 mm, and so slightly do the majority of the normally placed 

 germ-cells within the embryo vary from this, that it alone leads to 

 the suspicion of a certain definite number of mitoses from the first 

 origin to the long resting phase. Larger germ-cells in the normal 

 position — the site of the future germinal nidus — are rare, but 

 sometimes one does encounter them. One such is shown in fig. 8, 

 and its position is indicated by an asterisk in the diagrammatic fig. 6. 

 Its diameter is 0,036 mm. This size of germ-cell is more numerously 

 represented among those found wandering. These, as will appear, 

 also include many as large as 0,05 mm. Probably, if these larger 

 cells ever do get into the germinal nidus, their entry therein — and 

 this also coincides with their entry into the resting-phase — is accom- 

 panied by one or two divisions, as shown in fig. 26^ where one such 

 giant germ-cell has divided into four of the normal size. 



A prominent character of early germ-cells — at once a help and 

 a nuisance to the investigator — is the retention of yolk for a very 

 long period — long after it is used up in all the somatic cells (Nuss- 

 BAUM '80). Once more this is an indication how little prone they are 

 to enter into mitosis. In actively dividing cells the yolk is used up 

 very quickly. 



The yolk-plates are at first and for long after pretty numerous 

 in the germ-cells. As Eückert ('99) has pointed out in another con- 

 nection, they are of fairly equal size. Occasionally larger and smaller 

 plates are met with, as shown in some of the figures. Usually they 

 do not diminish in size as they are used up. Thus, in fig. 12, taken 

 from an embryo of 42 mm, the few remaining plates are as large as 

 in fig. 8, from an embryo of 7 mm. 



The yolk-plates finally disappear by the time the embryo is almost 



