EXTRACT XXV. A. 



ON THE EMBRYONIC DIFFERENTIATION, OR DIVISION 

 AND REUNION, OF THE NEURENTERIC CANAL, 

 WITH SOME ACCOUNT OF THE ALIMENTARY 

 CANAL AND THE PROCESS OF DIGESTION. 



THE neurenteric canal is one of the earliest embryonic 

 arrangements of the organic elements of the blastoderm, 

 and is the outcome of the initial differentiation and 

 structural arrangements of its several parts, the con- 

 tinuation of which is ultimately to culminate, by the 

 organisation of the total of these primary organic elements, 

 in the fully developed body. The organisation of the 

 embryo, at the stage of development represented by the 

 V-shaped neurenteric canal, is necessarily most rudi- 

 mentary, but still complete enough to meet all the vital 

 requirements of the embryonic body, and to form the 

 developmental basis, on which is to be constructed, the 

 future alimentary, and neural, systems, and the organs 

 of the succeeding nascent organism with their constantly 

 increasing facilities for inter-action and co-operation, in 

 the performance of the complex functional work of the 

 fully developed body. 



The division of the neurenteric tube into two neural, 

 and enteric, represents a great advance in embryonic 

 development, indicates the first step in the evolution of 

 a systemic nervous system, the dividing point, or line, 

 between sympathetically, and systemically, innervated, 

 creatures, and constitutes an entirely new departure from 

 the sequence of what, may be called, vegetative-life evo- 

 lutional phenomena. 



