( 800 ) 



Zoology. — "On gastrulation and the covering of the yolk in the 

 teleostean egg." By Dr. J. Boeke. (Communicated by Prof. 

 A. A. W. Hubrecht). 



(Communicated in the meeting of January 26, 1907). 



1. Generally the process of gastrulation in teleosts is described 

 by the greater part of the embryologists as a folding in of the margin 

 of the blastoderm and the forming, partly by this process of folding 

 and partly by delamination, of a mass of cells that contains the 

 elements both of the chorda and mesoderm and of the entoderm. 

 Only Waclaw Berent, M. v. Kowalewski (in his paper of 1885), 

 F. B. Sumner and myself have described a more or less independent 

 origin of mesoderm and chorda on one side and the entoderm on 

 the other side. Simnfh called the mass of cells lying at the posterior 

 end of the embryo, from which the entoderm originates, prostomal 

 thickening; I kept the same name for them and regarded these cells 

 as being derived from the periblast. 



The large pelagic eggs of Mnraenoids, which I could collect in 

 large quantities at Naples, offer an extraordinarily good object for 

 the study of these processes, much better than the eggs of Salmonides, 

 studied chiefly by French and German authors l ). The formation of 

 chorda and mesodermic plates out of the folded portion of the blas- 

 toderm, and of the entoderm out of the "prostomal thickening", the 

 mass of cells that lie at the hind-end of the embryo and are connected 

 with the superficial layer and with the periblast, is clearly to be 

 seen from the beginning of the formation of the embryo until the 

 closure of the yolk-blastopore (confirmed by Sumner in his paper of 

 1904) and after a renewed careful study of these eggs a ) I can only 

 confirm entirely and in full the conclusions arrived at in my former , 

 paper 3 ) and the observations described there at some length. 



But in accordance with the new and better definition of gastrula- 



1 ) Neither Henneguy, nor Kopsch or Jablonowski, to take a few examples, did 

 see anything of these differentiations. Sumner gives however of Salvelinus very 

 clear figures and descriptions. (Arch. f. Entwickelungsmech. Bd 17. 1903). 



2 ) During the last 2 or 3 years Muraenoid-eggs seemed to have disappeared 

 entirely from the Gulf of Naples. Now (summer 1906) I found them again in 

 sufficient quantities. When comparing the different eggs with each other, it seemed 

 to me that they belong to a still larger number of different species than I 

 concluded in my former paper (9), and that there must be distinguished at least 

 10 different species of Muraenoid eggs in the Gulf of Naples. Dr. Sanzo at Messina 

 came to the same conclusion. 



8 ) Petrus Camper, Vol. 2, page 135—210 1902. 



