646 JOHN BEARD, 



cells in the germinal nidus is very small, and there are very few on 

 the mesentery and within it. Many of the missing ones may be in 

 other parts of the embryo or in the yolk-sac. But actually engaged 

 in wandering there are few, the paucity of those on and in the mesen- 

 tery pointing in the like direction. In these respects the contrast 

 between the two embryos and No. 448 is very marked. Unlike 

 No. 454 neither of the two embryos contains a number of germ-cells 

 derivable from synchronous divisions of one or two cells. 



In these cases we possibly have an indication, that, even when 

 the wandering is finished, not all embryos contain the like number, 

 or even an approximation thereof, of primary germ-cells ^). 



VII. The Grerm-Cells of an Emhryo of 26 mm. 



Embryos of 25 to 27 mm possess the following external char- 

 acters. There are small external gills on all five branchial arches; 

 the unpaired fins, which first appear in embryos of 24 to 25 mm, 

 contain no mesoderm; the lateral line extends a short distance and 

 for not more than a fourth over the pectoral fins; the spiracle is 

 still elongated; there are no signs of an upj)er jaw; the nose is a 

 simple pit. 



R. batis No. 448 measured 26 mm in the preserved condition. A 

 few germ-cells were encountered in the normal position, but at the 

 extreme anterior end of the abdomen, and some distance in front of 

 the pronephros. Of these one or two were of about 0.036 mm, or 

 double the normal size. 



Apart from these there was a whole contingent, representing 

 perhaps a couple of dozen, in the liver. Some of these were of large 

 size, i. e., from 0.036 up to 0.05 mm, and many of them were multi- 

 nucleated. They lay in part between the splanchnopleural und hypo- 

 blastic portions of this organ, and extended thence inwards along the 

 line of these two layers, and then downwards between gut and 

 splanchnopleure in the yolk-stalk. 



In all my collection (of embryos of 25 — 27 mm there are sec- 

 tions of not fewer than 12) -) this is the only instance, in which such 

 germ-cells have been seen in the liver. But no close search has been 



1) From more recent and as yet unpublished researches it is pro- 

 bable, that these two embryos were potential males with a maximum 

 number of 255 primary germ-cells. 



2) In 1900. 



