294 ANIMAL PHYSIOLOGY. 
It is plain that if, in the digestive tract, foods are changed 
in solubility and actual chemical constitution, this must have 
h 
Fic. 249.—Alimentary canal of embryo while the rudimentary mid-gut is still in continuit 
with yelk-sac (K6lliker, after Bisc sets A. View from before. a, pharyngeal Plates ; if 
pharynx ; c, ¢, diverticula forming e lange 5 d, stomach ; f, diverticula of liver; g. 
membrane torn from yelk-sac ; h, hind-gut. B. L 
ongitudinal section. a, diverticulum o! 
alung; b, stomach; ¢, liver; d, yelk-sac. 
been brought about by chemical agencies. That food is broken 
up at the very commencement of the alimentary tract is a 
matter of common observation; and that there should be a 
gradual movement of the food from one part of the canal to 
Fia. 251. 
Fic. 250.—Diagram of alimentary canal of chick at fourth day (Foster and Balfour, after 
Gétte). 1g, diverticulum of one lung; Sz, stomach ; 1, liver ; p, pancreas. 
Fig. 251.—Position of various parts of alimentary canal at different stages. A. Embryo of 
five weeks. B. Of eight weeks. C. Of ten weeks (Allen Thompson). 1, pharynx with the 
lungs; s, stomach ;,2, small intestine ; 7’, large intestine; g, genital duct; u, bladder; 
cl, cloaca; c, cecum ; vi, ductus vitello-intestinalis ; si, urogenital sinus ; v, yelk-sac. 
