760 SUMMARY OF CURRENT RESEARCHES RELATING TO 



(and results from) the disappearance of the peculiar marginal thick- 

 enings which the blastoderm, since losing its lenticular figure, has 

 hitherto presented. While the mesoblast coincided in extent with the 

 ectoderm, it most abounded in the hinder and outer regions of the germ, 

 being more sparingly manifest anteriorly and in the area pellucida. 

 But with the formation of the primitive streak a rapid centripetal 

 migration of the middle-germ ensues, and its cells retreat within the 

 limits of the clear area. Much confusion prevails as to the use of the 

 phrases — marginal protuberance, germinal wall and germinal protu- 

 berance. The " Keimwall " of His belongs to the white yolk. It is 

 identical with the " Keimwulst " of Kolliker, which, however, the 

 latter views as synonymous with the " Bandwulst " of Goette. But 

 this lies wholly outside the white yolk, and is made up of the residual 

 cells between it and the outer lamina. 



Bemak first instituted the conception of germinal laminae as at 

 present understood. [To a certain extent he was anticipated by 

 C. F. Wolff and von Baer.] He was tolerably right as to his facts, 

 but erred in his deductions. Unacquainted with the cleavage of the 

 hen's egg, he could not well appreciate its constitution before the 

 formation of the ectoderm, nor could he perceive the significance of 

 the germinal layers in the development of the higher animals 

 generally. He describes the germ of the unincubated egg as made 

 up of a firm outer and a more loosely constructed inner lamina. 

 From the latter, as a first result of incubation, his alimentary glan- 

 dular lamina separates by transformation of its cells. The residue of 

 the inner lamina is now the middle lamina. Apart from this deriva- 

 tion, at least nominally, of one germinal lamina from another, he 

 finally has at his disposal a middle and an outer lamina but not an 

 inner ; since his first inner lamina is resolved into the middle and 

 the alimentary glandular lamina, which latter alone he deems the 

 earliest rudiment of a definite system of organs. Bemak's interpre- 

 tation had many followers. They differ from him in words only who 

 derive a middle lamina from his inner lamina and give this name to 

 Bemak's " Darrndrusenblatt." It is all the same whether a splits 

 from b, or b from a. 



This " Darmdriisenblatt " is the inner lamina of Kolliker. What 

 remains of the germ constitutes the outer layer, in Kolliker's sense. 

 From it, therefore, he derives his middle lamina, which is formed by 

 the extension of masses of cells from the region of the primitive 

 streak, on both sides of the germ, between its ectoderm and endoderm. 



Goette is right in describing a previous transfer of cells from the 

 marginal protuberance, centripetally. But this wandering does not 

 take place until after the formation of the inner layer. The 

 migrating elements are cells of the middle-germ, and together with 

 the cells of the primitive streak they make up the axial plate. The 

 inner germinal stratum of Goette, which divides into his inner and 

 middle laminae, is equivalent to the first inner lamina of Bemak, who 

 sometimes also designates this as the inner " Keimschicht." 



Beremeschko, like Kolliker, is wrong in believing that in the 

 formation of the ectoderm and endoderm the whole substance of the 



