652 JOHN BEARD, 



RücKERT ('87). These may be also present in other places. Their 

 probable nature will be discussed in another section. 



X. The Germ-Cells in the earliest Period of Emhryo- 



Formatioii. 



Under this heading it is proposed to consider the distribution of 

 the germ-cells at a time, when the parts of the embryo already ap- 

 parent have no great extension. The period included embraces the 

 interval from the formation of the first mesoblastic somite until about 

 fourteen are laid down. 



Embryonic foundations with 1 to 14 somites contain practically 

 no germ-cells, or at most but one or two; and, therefore, one cannot 

 properly speak of the germ-cells of "embryos" with any number of 

 somites not greater than the above. In no instance, where there 

 were less than 12 somites, have I found any germ-cells within the 

 embryonic foundation. As, therefore, the germ-cells have not then 

 commenced their migrations into the embryo, there would be slight 

 gain to be obtained from detailed descriptions. Moreover, the con- 

 ditions observed, apart from the total absence of germ-cells within 

 the embryonic foundation, resemble those encountered in the example 

 with 12 somites about to be described. That is to say, in these 

 younger phases all the germ-cells are within the blastoderm. 



In Raja batis No. 691 {2.66 mm) there appeared to be about 12 

 somites laid down. They were somewhat indistinctly made out, for 

 the yolk on the underside of the blastoderm was not cleared away to 

 to any great extent, because of the danger of removing other things 

 with it. The medullary plate was spoon-shaped in form, measuring 

 about 2.66 mm in the preserved condition. As shown in the two 

 text- figures (A and B) the medullary folds are raised in section. 



In the anterior part of the blastoderm in front of the embryonic 

 foundation the large heap of cells of the pre-embryonic period is still 

 represented. These cells are of much interest. Their sizes are those 

 of "megaspheres" and true germ-cells, that is to say, on an average 

 about 0.05, 0.03, and 0.02 mm. There are very many of the latter 

 size. Not only do they resemble normal germ-cells in size, but their 

 appearance is the same, their cytoplasm has the like glassy character, 

 they contain the like amount of yolk and the plates of this are of the 

 sizes found in the normal primary germ-cells of later periods. Many 

 of them appear to be in amoeboid motion. Multinuclated ones were 



