668 - JOHN BEARD, 



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

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



Others of the germ-cells in a certain position, 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 presented 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 surmised 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. hatis for purposes of nutrition, until 

 the young fish has a length of 65 — 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, do 

 degenerate by one or other of two processes ; these are simple atrophy 

 and the formation of cell-nests or "concentric corpuscles". In both 

 "chromatolysis" is exhibited. But so far this degeneration has been 

 verified in few of them , though it has been observed in several 

 embryos. One may surmise, that as a general rule the remaining 

 vagrant germ-cells undergo a like fate. The writer cannot believe, 

 that the large number found on the mesentery in older embryos (in 

 No. 454 there were 110, in No. 448 even 120) will ever find their 

 way to the germinal nidus, or that they usually remain for a long 

 period unaltered in their abnormal situations ^). 



It is also recorded, that in Raja radlata No. 268, a young skate 

 and the equivalent of a R. hatis of 70 mm, none were found on the 

 mesentery. It might repay the labour to study minutely phases from 

 45 to 70 mm or older. At the other end of the scale there is the 

 cleavage also clamouring for investigation. It is, indeed, the good 



1) Vide Section XIII, page 672. 



2) Since writing the above the degeneration of many such germ- 

 cells has been observed. 



