SOME POINTS IN EARLY DEVELOPMENT OF HEN's EGG. 163 



The eggs alluded to offered such a favorable opportunity 

 for the study of the relation of the germ to the subger- 

 niinal finely granular layer, that we shall discuss this rela- 

 tion in connection with these eggs first before referring to 

 normal eggs. 



The point that we are endeavouring to prove in this 

 part of the present paper is that the finely granular sub- 

 germinal layer is richly nucleated^ and gives rise to nu- 

 cleated masses which are separated from this layer previous 

 to the formation of the subgerminal cavity, and become fused 

 with the germ (as in fig. 6) ; later on they constitute the 

 well-known " formative cells " or " Dotterzellen " (Goette), 

 which are seen on the floor of the segmentation cavity after 

 the appearance of that cavity. 



Before describing in detail our own observations on these 

 relations, we shall mention shortly the results obtained by 

 previous observers on these points. His was the first to 

 suggest that the embryo is not exclusively developed out of 

 the blastoderm proper, and asserted that the white yolk 

 took a prominent part in the development of certain 

 tissues of the embryo, particularly the blood. He de- 

 scribed the blastoderm proper as the archiblast or " Haupt- 

 dotter," and the white yolk as parablast or " Nebendotter." 

 Though it is generally admitted that the conclusions 

 of His were inaccurate, inasmuch as nearly all subsequent 

 observers deny that the white yolk participates in segmenta- 

 tion, yet these observations probably directed the attention 

 of later workers on the hen's egg to the existence of a very 

 finely granular layer, " the subgerminal layer," forming the 

 superficial surface of the white yolk beneath the blastoderm. 

 At any rate, the importance of this layer has been shown to 

 be very great in the eggs of Fishes by Bambeke, Klein, and 

 Balfour, as will be mentioned presently. 



Waldeyer was unable to decide whether the large forma- 

 tive cells or masses lying on the floor of the subgerminal 

 cavity arose from the white yolk or not, but agreed with His 

 in so far as he contrasted the products of segmentation of the 

 blastoderm with the eventual products of white yolk. Wal- 

 deyer distinguished a " Hauptdotter" and a " Nebendotter " 

 like His, and described the products of segmentation of the 

 former only (viz. blastoderm) as primary descendants of the 

 ovum. 



Peremeschko (* Strieker's Histology,^ vol. iii, p. 527, Eng. 

 edition) states that the large granular cells in the floor of 

 the subgerminal cavity increase considerably in number in 

 the first hours of incubation. And since, he urges, this 



