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ferently interpreted by him. The result of their recognition by Lwoff 

 was that he maintained the formation of a dorsal plate, his ecto-blasto- 

 genetic plate and therefore described the notochord as being of ecto- 

 dermal origin. Hübrecht sees the same dorsal plate and in it he 

 lands confirmation of Sedgwick's views of a drawn out actiniau stomo- 

 daeum and calls it Notogenesis. To the part which is formed first 

 HuBRECHT gave the name of Kephalogenesis (Furchung und Keimblatt- 

 bildung bei Tarsius Spectrum, 1902) but in his present paper (Anat. 

 Anz., 15. March 1905) he restricts the term to "that very foremost 

 region of the head to which Ophthalmicus and Opticus belong". 



Now both Lwoff and Hubrecht take no notice of what I believe 

 to be the essential feature of these two growth centres, namely, that 

 the secondary or more posterior of the two is a growth centre which 

 adds on new material not only dorsally but laterally and 

 ventrally as well. Also this secondary centre of growth arises 

 subsequently to the first, and is to be regarded as representing 

 a phylogenetically more recent period. 



If these facts are appreciated then away goes the difficulty of the 

 apparent ectodermic origin of notochord because Lwoff's ectoblasto- 

 genetic plate has nothing whatsoever to do with "gastrulation", but is 

 the subsequent growth in length of the animal representing a post- 

 gastraea or post-coelenterate epoch, and many of the apparent incon- 

 sistencies in the origin of organs from the germinal layers in verte- 

 brates disappear. 



Again, much of the embryological support to Sedgwick's theory 

 of an elongated gastrula mouth so far as Vertebrates are concerned, 

 restated by Van Beneden and Hubrecht, is thereby lost. 



But I will leave theory and phylogeny alone for the moment and 

 appeal to experimental observation. 



My former work on the rabbit, in which I first used the terms 

 "primary centre of growth", and "secondary centre of growth", was 

 done by old methods entirely. 



The work on the Frog and the Chick was experimental. Fortunately 

 the Frog is a beast peculiarly amenable to experiment — from the 

 egg to its old age. (Schluß folgt.) 



