286 BASHFORD DEAN. 



and its appropriation by external gills l (and gut). This process 

 is an important one from a larger aspect since it yields a mode of 

 nutriment hitherto unknown in vertebrate embryology-- a proc- 

 ess by which a late embryo appropriates as food, in the ordi- 

 nary acceptance of the term, an outlying portion of its own 

 organism. 



(C) The mode of development of mesenchyme from yolk- 

 nuclei in a somewhat similar way as described by Riickert for 

 selachians. 



1 The origin of the latter process is suggested on the following lines : The gills lying 

 in close contact with the egg came to absorb nutriment from the neighboring finely 

 divided blastomeres and from the interblastomeral fluid. And the embryo came to 

 employ the peripheral yolk more promptly and efficaciously thus than in the ancient 

 way, with the result that the peripheral blastomeres became more loosely associated 

 and finally separated. These melt ultimately into a creamy fluid especially adapted 

 for providing nutriment for the specializing gills of the embryo. 



