ORGANS OF DIGESTION. 



335 



organs which move laterally and are provided with palpi ; 

 and hard parts subservient to this function are often found 

 in the cavity of the stomach. The mucous lining of the 

 alimentary canal exhibits few developments of villi, folds, 

 or follicles, the salivary and pancreatic glands are rarely 

 perceptible, and the liver has generally the simplest folli- 

 cular form. 



VI. Entozoa. The entozoa, subsisting on the living 

 fluids of animals more highly organized than themselves, 

 present generally the simplest condition of the alimentary 

 apparatus met with in the articulated classes, and from the 

 facility of assimilating the nutritious fluids which they 

 absorb, many of these animals dispense with a separate anal 

 orifice, and their digestive organs are thus often closely 

 approximated in form to the vascular or sanguiferous sys- 

 tem. In the cystoid forms of intestinal worms, as in the 

 simplest polypi, there is only , a buccal entrance to the di- 

 gestive sac, and that orifice is often numerously repeated 

 on the same sac, like the polypi of a zoophyte or the absor- 

 bent orifices of a rhizostome. In the hydatids, as in the 

 hydras, there is a simple digestive cavity destitute of an 

 anal aperture, but here, as seen in the cysticercus longicollis 

 (Fig. 116, A.), the buccal apparatus (A. a. b. c.) } is in form 



d 



