610 THE REPRODUCTIVE FUNCTIONS. 



the wants of the system, has accumulated round 

 the embryo ample stores of nutritive matter, suf- 

 ficient for maintaining the life of the chick, and 

 for the building of its frame, while it continues 

 in the egg, and is consequently unable to obtain 

 supplies from without : yet, with the same fore- 

 sight of future circumstances, she delays not, 

 longer than is necessary for the complete esta- 

 blishment of the circulation, to construct the 

 apparatus for digestion, on which the animal is 

 to rely for the means of support in after life. 

 The alimentary canal, of which no trace exists 

 at an earlier period, is constructed by the for- 

 mation of two laminae, arising from folds of the 

 innermost of the pellicles which invest the 

 embryo ; that is, on the surface opposite to the 

 one which has produced the spinal marrow. 

 These laminae, which are originally separate, 

 and apart from one another, are brought toge- 

 ther, and by the junction or soldering of their 

 opposite edges, formed into a tube,* which, from 

 being at first uniform in diameter, afterwards 

 expands into several dilated portions, corre- 

 sponding with the cavities of the stomach, crop, 

 gizzard, &c. into which they are to be converted, 

 when the time shall come for their active em- 

 ployment. These new organs are, however, even 

 in this their rudimental state, trained to the per- 



* Wolff is the author of this discovery. 



