The germ-cells. QQ'J 



the latter, in the same embryo 110, find a resting place somewhere 

 on the mesentery to the ventral side of the nidus, and, it may be, as 

 low down as the subintestinal vein (Figs. 16 and 21) or even on the 

 opposite wall. As already seen, in embryo No. 454 only some 53 

 probably failed to follow the germinal path^). 



The wanderings of some of the germ-cells would appear to con- 

 tinue for a relatively long period of the development. At any rate, 

 they are met with between splanchnopleure and gut, as well as in 

 other places, in embryos of 14 to 17 mm, or even of 20 mm. For 

 some time after this latter period, apart from those which have got 

 into impossible places, one meets with amoeboid germ- cells only in 

 the connective tissue above and around the gut. The gut is now 

 shut off from the yolk-sac, and to this period dates the first appear- 

 ance of a narrow yolk-stalk, connecting embryo and yolk-sac. That 

 is to say, the embryo is now well raised up from the yolk-sac. 



At least until the embryo is 42 mm the primary germ -cells remain 

 quiescent. They gradually use up their yolk, retaining, however, their 

 average size of 0,02 mm. The secondary ones are smaller 

 (Fig. 33). 



In the preceding pages it has been shown, that vagrant germ-cells 

 are found in all sorts of places, but more particularly on the mesen- 

 tery, including the whole of the splanchnopleure, even in embryos of 

 42 mm. Later on they have not been found. Whether they degenerate, 

 or migrate into the germinal nidus, or whether some, or a majority 

 of them persist in abnormal situations, has not at present been de- 

 termined. Even in embryos of 42 mm and younger the large germ- 

 cells of 0.036 to 0,056 mm have, so far as my observations go, com- 

 pletely disappeared. Some of them, doubtless, have gone through 

 the failing division, or two or three such mitoses, which were 

 wanting to bring them down to the normal size, thus Fig. 26. This, 

 however, will depend on their situation. 



The large multinucleated ones, which have not been encountered 

 in every embryo, doubtless degenerate and disappear. Many indi- 



1) The above is given as a typical example, other cases will be 

 found in the descriptive part of the memoir and still others will be 

 given in Parts II and III. It may be added, that in all probability the final 

 definite number of normally placed primary germ-cells is subject to 

 variations. Moreover, germ-cells may degenerate at any period of the 

 life-history. These variations are sufficient to account for wide differ- 

 ences in the virility of different individuals. 



Zool. Jahrb. XVI. Abth. f. Morph. a a 



