MaiicJiester Memoirs, Vol. I. ( 1 906), No. 3. 3 



gists, I mean the relation of the Amniote blastopore to 

 that of the Anamnia.- 



Fatal, however, as I believe the evidence of Vertebrate 

 development to be to the common views, the testimony 

 available from other sources must also be taken into 

 account ; I have, therefore, supplemented my critique by 

 a consideration of the embryogeny — in particular of the 

 cell lineages — of various Invertebrates, and of the bearing 

 of all the facts of budding, regeneration, pathology, and 

 experimental embryology on the problem. 



The conclusion to which I have come I have already 

 hinted at ; unacceptable as it may prove to many, it is 

 the onl}^ conclusion which, as far as I can see, is compatible 

 with the facts.^ 



Part I.— THE GERMINAL LAYERS OF THE 

 VERTEBRATA. 



ANAMNIA. 



As a type of the formation of the germinal layers in 

 the Anamnia, I will take the form which has been most 

 extensively studied, and with which I am myself most 

 intimately acquainted, the common English Frog {Rana 

 temporaria). 



Let me say at the outset that I define these layers — ■ 

 the ectoderm, the endoderm, and the mesoderm — solely 

 with reference to their destiny;* by the "ectoderm" I 



- A complete literature of the germ-layers of the vertebrates will be 

 found in Hertwig's " Handbuch " Cap. 3, (Gustav Fischer, Jena, 1903) ; 

 to this the reader is referred for particulars of the memoirs quoted in the 

 present paper. 



" Since this paper was written I have found that F. Braem, in a paper 

 entitled " Was ist ein Keimblatt ? " and published nearly ten years ago {Biol. 

 Centralblalt, vol. 15, 1895, P- 427— 443> 466—476, 491 — 506), came to 

 conclusions practically identical with my own. Braem's views are founded 

 mainly on the developmental phenomena of Bryozoa and Ascidia. 



•'Braem's phrase deserves quoting: " Keimblatter," he says, *' sind 

 Organbildner." (p. 431.) 



