The germ-cells. 659 



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

 sition and general characters, are many of those of Plate 43. 

 The usual size of such is 0.02 mm, and so slightly do the major- 

 ity 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. 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 accompanied 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 

 (NUSSBAUM, '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 Rückert ('99) has pointed out in another con- 

 nection, they are of fairly equal sizes. 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 

 complete and possessed of all the characters of a young skate, thus, 

 in an embryo of 54 mm (Fig. 33) they are quite gone. 



The cytoplasm of the early germ-cells, large and small, no 

 matter where they be, is very peculiar. It is a colourless, glassy 

 substance, possessing no affinity for any of the ordinary stains. 

 Osmic acid tinges it of a slightly brownish hue. Rarely in early 

 stages are the cells rounded, unless they be in a position of rest, 

 among a mass of other cells, or encapsuled in some peculiar position. 

 More usually they are irregular in form, and show processes, which 

 can only be defined as amoeboid. Though their actual movements 



