102 THE VITAL FUNCTIONS. 



ferent 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 Lufiibricus 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 sto- 

 machs, backwards and forwards many times, 

 before its digestion is accomplished. 



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, 



