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, j \^" j^j 



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 which 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 or ventriculus receives the food immediately 

 from 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 ^y 

 food, for it immediately undergoes a change in consistence 

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

 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 L 

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

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



