OF THE ALIMENTARY CANAL. 185 



oesophagus is the part which most nearly approaches the 

 head, and the external opening of which is the throat or 

 pharynx already described ; it is of various length ; and 

 in this particular it appears more influenced by the variation 

 of external form than by the quantity or quality of food 

 consumed. The gullet is called simple or simplex when 

 it is merely a tube of uniform size extending from the 

 pharynx to the entrance of the stomach : this is the usual 

 structure. It is ventricose or ventricosus when it dilates 

 into a large bag or crop before its union with the stomach, 

 and detains the food in its passage to that organ. It is 

 said to be compound or compositus when it has a long 

 pear-shaped cell opening from it, and extending beneath 

 the stomach and intestines, yet having no communication 

 with either ; this is the case in all the flies and gnats which 

 feed on blood, and many of the same tribes wliich subsist 

 on other fluids : the blood sucked is at once received into 

 it ; and, as enough is frequently swallowed at a single meal 

 to last for days, it returns slowly to the gullet as required, 

 and then passes to the stomach for digestion. 



The stomach ov-ventriculus receives the food immediately 

 fi'om the gullet, digests it, and passes it on to the intestines. 

 The food immediately on entering the stomach, combines 

 with, and is pervaded by, some fluid secreted by the sto- 

 mach ; this fluid probably serves to assist in digesting the 

 food, for it immediately undergoes a change in consistence 

 as well as colour. The stomach varies greatly in the fonn 

 and nature, both of its main cavity, and of the numerous 

 appendages with which it is occasionally furnished. It is 

 termed simple or simplex when it is a mere continuation of 

 the gullet in an enlarged form, being slightly constricted at 

 the union with the gullet, and more so at its junction with 

 the intestines, where an elastic ring is placed, which, when 

 contracted, nearly closes the aperture. It is said to be 



