345 



it possible that a considerable length of anterior part of the nervous 

 system is formed in the black hemisphere, and with Pflüger I quite 

 agree on this point." 



The earlier experiments on Amblystoma by the present writer^) 

 led to the following deductions: "Firstly, an area at the apical pole 

 of the egg forms the basis of the head of the embryo. Secondly, an 

 area at the dorsal lip of the blastopore lies in the posterior half of 

 the embryo. Consequently the anterior half of the embryo, at least, 

 is formed from the material lying between the apical pole and the 

 dorsal lip of the plastopore." 



Later experiments '^) on the eggs of Rana, Bufo, Acris and Ambly- 

 stoma, led to these conclusions: 



"The primary area of cell activity, at the upper pole of the egg, 

 forms the basis of the cephalic end of the embryo. 



The secondary area of cell activity, on the blastoporic side of 

 the egg, forms the basis of the greater portion of the posterior half 

 of the embryo. 



These two areas constitute an embryonic tract, from which arises, 

 at least, the anterior two-thirds of the embryo. 



The posterior end of the embryo is formed by a coalescence of 

 the lateral portions of the blastoporic margin. 



The greater portion of the embryo arises in the 

 darker hemisphere by differentiation in situ, and not 

 by concrescence." 



H. V. Wilson has most recently extended these experiments to 

 the eggs of Chorophilus and other forms ; their significance is interpreted 

 as follows : "My own experiments led to such apparently contradictory 

 results that I was inclined to take Schultze's view of the method. 

 After comparing and classifying my experiments, however, it seems to 

 me the results are all explicable on the theory advanced by Assheton, 

 Whitman and Eycleshymer, that the dorsal and ventral lips overgrow 

 the yolk, from the place of their first appearance to the lower pole 

 — the neural plate hence being formed in part on the black hemi- 

 sphere and in part by the backward growth of the dorsal lip over the 

 white hemisphere, as PflIIger thought was possibly the case." 



With a hope of throwing more light upon some of the processes 

 involved in the formation of the Amphibian embryo a series of ex- 



1) The Early Development of Amblystoma, etc. Journ. Morphol. 

 Boston, Vol. 10, 1895, p. 340—418, 5 pi. 



2) The Location of the Basis of the Amphibian Embryo. Journ. 

 Morphol. Boston, Vol. 4, 1898, p. 467—480, 100 figures in text. 



