164 p. KIDD. 



increase in number is unaccompanied by any diminution in 

 size, it becomes highly probable that the cells projecting 

 downwards from the inferior lamina of the blastoderm fall to 

 the bottom of the cavity. 



Subsequently, Oellacher and Klein confirmed Peremesch- 

 ko's observations on these points. 



Balfour and Foster (' Elements of Embryology ') in the 

 first chapter on the unincubated egg, give it as their opinion 

 that these formative cells may arise as Peremeschko, 

 Oellacher, and Klein stated, or might arise from the upper 

 part of the white yolk. However, later on when segmenta- 

 tion is more advanced, after incubation has commenced, they 

 seem to declare themselves in favour of the latter opinion, 

 without, however, giving any very positive arguments in 

 favour of such an opinion. 



Goette, in a very important memoir (*Max Schultze's 

 Archiv, ' Bd. x, p. 145), returning to a certain extent to the 

 views of His already mentioned, draws attention to the 

 subgerminal finely granular layer separating the germ from 

 the white yolk in the earlier stages and forming the floor of 

 the subgerminal cavity later on. He describes the sub- 

 germinal layer as white yolk. Goette agrees with Oellacher 

 that segmentation proceeds gradually from the surface towards 

 the deeper parts of the germ. The blastoderm, according to 

 Goette, segments rapidly and early, whereas segmentation 

 appears later on in the white yolk. The white yolk undergoes 

 cleavage and separates into large masses, the " Dotterzellen " 

 or formative cells which subsequently appear on the floor of 

 the segmentation or subgerminal cavity. These are Goette's 

 opinions, and he gives the following observations in favour 

 of these views. 



In the finely granular upper layer of the white yolk Goette 

 found nuclei here and there, resembling the nuclei of the 

 segmentation cells in character. In the neighbourhood of 

 these nuclei there were to be seen occasionally indications of 

 cleavage, which he regarded as due to a continued process of 

 segmentation. Goette finds that the floor of the segmenta- 

 tion cavity, from its first appearance until incubation begins, 

 continues to give rise to fresh nucleated masses, or " Dotter- 

 elemente," as he calls them. Some of these elements were 

 seen to rise as papilliform elevations of the floor of the sub- 

 germinal cavity. Various stages could be observed from a slight 

 elevation of the surface of the floor, to the formation of more or 

 less bud-shaped processes attached to the white yolk by a thin 

 neck. In some, but not in all cases nuclei could be observed 

 in these large masses. Goette thinks it possible or probable 



