476 



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

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

 (fig. 33) 0. 



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

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

 mesentery, including the whole of the spanchnopleure, even in embryos 

 of 42 mm. Later on they have not been found. Whether they de- 

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

 majority of them persist in abnormal situations, has not at present 

 been determined. Even in embryos of 42 mm and younger the large 

 germ-cells of 0,036 to 0,05 mm have, so far as my observations go, 

 completely 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 indications 

 of this have been seen. Some of them are described in the general 

 part, but these are only a fraction of the many examined. 



Others of the germ-cells in a certain postition, i. e., the gut-epi- 

 thelium, seem to be always doomed to degeneration. Their migration 

 from the gut into the mesoblast has been searched for again and 

 again, but in vain. 



Wandering germ-cells are often found within the mesentery, quite 

 close to the gut, in embryos of upwards of 18 mm ; but, although their 

 migration outwards from the gut-epithelium might be suspected, it has 

 not been established. On the other hand, abundant evidence has pre- 

 sented itself of the elimination of these germ-cells in another direction, 

 into the gut-cavity. Frequently whole cells have been found there, 

 oftener one encounters parts of them, laded with yolk. Indeed, it 

 may be suspected that a degeneration, similar to that described in 

 the account of certain embryos, with formation of cell-nests and a 

 separation from the yolk, may occur here. It would also account for 

 the yolk in the gut-cavity at this period ; for yolk from the yolk-sac 

 does not enter the gut of R. batis for purposes of nutrition, until the 

 young fish has a length of about 70 mm. The yolk-plates are then 

 much larger. 



It has been established, that some of the vagrant germ-cells, 

 more particularly those in the body-cavity and the multinucleated ones, 



1) Balfour (78, 2) states that they are larger! 



