102 THE VITAL FUNCTIONS. 



rent parts of the canal ; this is the case with the 

 intestine of the Aphrodita aculeata, or sea-mouse. 

 The intestine, being generally longer than the 

 body, is obliged to be folded many times within 

 the cavity it occupies, and to take a winding 

 course. In some cases, on the other hand, the 

 alimentary tube passes in nearly a straight line 

 through the body, with scarcely any variation in its 

 diameter ; this is the case with the Ascaris, which 

 is a long cylindric worm ; and nearly so with the 

 Lumhricus terrestris, or earth-worm. In the Nais, 



on the contrary, as shown 

 in Fig. 259, the alimentary 

 tube presents a series of 

 dilatations, which, from the 

 transparency of the skin, 

 may be easily seen in the 

 living animal. The food taken in by these worms 

 is observed to be transferred from the one to the 

 other of its numerous stomachs, backwards and 

 forwards many times, before its digestion^ is ac- 

 complished. 



The stomach of the Leech is very peculiar in 

 its structure : its form, when dissected off, and 

 removed from the body, is shown in Fig. 260. 

 It is of great capacity, occupying the larger part 

 of the interior of the body ; and its cavity is 

 expanded by folds of its internal membrane into 

 several pouches (c, c, c). Mr. Newport, who 

 has lately examined its structure with great care, 



