ON THE STAGES OF EVOLUTION 225 



among which, gastro-enteric areas, for general, as well as 

 special, treatment of the alimentary materials, are pro- 

 vided, and thus, follow each other, the oral lock, the 

 pharyngeo-cesophageal, the cardiac, the pyloric, the ileo- 

 caecal, the sigmoid, and the anal, locks, with the intervening 

 digestive spaces, the oro-pharynx, the oesophagus, the 

 stomach proper, the duodeno-jejuno-ileal intestine, the 

 caeco-colonal bowel and the rectum. Each of these canal 

 divisions, or digestive areas, is provided with a series of 



FIG. 87. OUTLINE OF THE EMBRYO-CHICK AT THE END OF THE THIRD 

 DAY, TO SHOW THE INFLECTIONS OF THE BODY AND THE COMMENCE- 



MENT OF THE LIMBS. (After His.) 



i to 5 the cerebral vesicles ; b, the mouth ; mn, the lower jaw, and behind that the 

 branchial bars and clefts ; , the auditory vesicle ; h, the heart ; ae, anterior 

 extremity ; pe, posterior extremity ; the hinder part of the body is still prone upon 

 the surface of the yolk, the head is now lying on its left side and between is seen 

 the gradual torsion of the vertebral column and trunk. 



secretional fluids, and more or less absorptional machinery, 

 whereby the prolonged and complicated process of di- 

 gestion, is fully effected, and the irreducible residuum 

 returned to the outer world. We may take it, moreover, 

 that each of these digestive stages represents a specific 

 form of digestion, in which certain alimentary articles are 

 treated, and that the whole of them are required, to meet 

 the necessities of a complex digestive' process, such as, 

 undoubtedly, is present in man. The oro-pharyngeal 

 digestion may be described as preparatory, but most 

 important, in that the saliva from six different glands, 



