642 JOHN BEARD, 



ing account of the magnification (750 diameters), they are of the 

 normal size. In this embryo there is much yolk in the epiblast, little 

 or none in the pericardial cells. The former layer is not yet doubled. 

 A few sections further on there are two others in a like ventral 

 position. In Fig. 29 there is depicted a large amoeboid germ- cell 

 between splanchnopleure and gut. Fig. 23 furnishes an example of a 

 germ-cell, lying at the extreme ventral hmit of the peritoneum. 

 Fig. 24 is taken from a transverse section, just posterior to the pro- 

 nephros, and in it a germ-cell, migrating between splanchnopleure 

 and gut, is seen. In Fig. 25 there is one partly encapsuled within 

 the gut-epithelium. Fig. 26 depicts a group, formed by two divi- 

 sions of a larger one; it lay in the position of that shown in 

 Fig. 24. 



Two others, lying beneath the epiblast of the pericardial region, 

 are shown in Fig. 27. Fig. 29 may be compared with Fig. 26. It 

 demonstrates^) a phase, previous to the two divisions, which resulted 

 in the four cells of the latter. The position of this large cell is 



the same. 



The germ-cell of Fig. 34 lay just beneath that shown in Fig. 25, 

 and in the same section. It is drawn in the act of migrating through 

 the splanchnopleure. The example, found in Fig. 35, was found free 

 in the body-cavity. 



Lastly, Fig. 36 represents the third of five sections through a large 

 germ-cell, lying between gut and splanchnopleure. 



V. The Germ-Cells in an Embryo of 14 mm. 



The embryo, Raja hatis No. 634, was difficult to measure owing 

 to its curvature. It was estimated to be about 14 mm, but possibly 

 it slightly exceeded this. 



Externally. 5 gill-clefts were indicated, possibly a 6th pouch is 

 present internally. The beginnings of external gills were seen on the 

 3 anterior branchial arches. 122 somites were counted, but this number 

 is not guaranteed to be correct. 



The description of an older embryo has been reverted to, because 

 in at least two important points it presents a marked contrast to 

 those just considered. The normally placed germ-cells of this embryo, 

 which is a remarkably fine one, have not been counted. The wander- 



1) The cell of Fig. 29 is, however, the equivalent of 8, if not of 

 16, primary germ-cells. 



