GEOWTH IN LENGTH OF THE FROG EMBRYO. 223 



On the Growth in Length of the Prog Embryo. 



By 

 Richard Asslietou, M.A. 



With Plates 23 and 24. 



In some previous papers on the development of the rabbit I 

 have attempted to show that there are two main centres of 

 growth, each in itself tending to produce a radially symmetrical 

 form; but since these two centres of growth are situated 

 eccentrically to each other the resulting embryo is cylindrical, 

 and subsequently bilaterally symmetrical. 



I endeavoured to show that no concrescence occurred in the 

 rabbit, and that no theory of concrescence was necessary to 

 account for the facts. 



I wish now to indicate the manner in which two centres of 

 growth can also bring about the corresponding results in the 

 frog embryo, without any concrescence of the dorsal lips of the 

 blastopore. 



In a paper in this Journal Dr. Robinson and I discussed the 

 question of the formation of the archenteron in the frog, and 

 came to the same conclusion as Moquin-Tandon (in Anura) 

 and Houssay (in Axolotl), that the archenteric cavity was due 

 to a splitting amongst the cells in situ, and not to an invagi- 

 nation or overgrowth of surface cells. 



Recently Jordan, and Ume Tsuda and Morgan have made 

 very interesting communications upon the subject. 



The former author, after an able summing up of the evidence 

 on both sides, concludes (p. 331), "The evidence thus far adduced 



