LESSON 33.] NUTRITION IN THE ANNELLATA. 



119 



their native element, they thrust their respiratory organs (c) far 

 above the head, the vibra- FlG . 193 . 



tile cilia being, at the 

 same time, in rapid mo- 

 tion. But if any thing 

 chance to disturb them, 

 the respiratory tuft is 

 instantly withdrawn into 

 the tube (a) in which the 

 body is contained, and 

 the conical plug (5), form- 

 ed like the shell, of car- 

 bonate of lime, but cov- 

 ered with flesh, is drawn 

 tightly down, and effect- 



,-, -i ,1 Serpula coutortuplicuta. 



ually closes the entrance 



to the tube. At the top of the conical plug a pair of forcipated 

 instruments are placed ; it is their func- FIG. 199. 



tion to collect sand, and " puddle " it 

 down, so that it fill entirely the concave 

 summit with a compact layer of sand ; 

 by this expedient they frequently es- 

 cape molestation by even pretty good 

 naturalists, who affirm that " the ani- 

 mal is dead, and the shell filled with 

 sand." 



554. Much uniformity of plan pre- 

 vails in the structure of the nutri- 

 mental organs in this class, consisting 

 for the most part of a tube, generally 

 possessing enlargement of the gastric 

 cavity (stomach), which passes straight 

 through the body. 



555. In some of the higher worms, 

 as in the Sea-mouse (ApJirodita acu- 

 leata), the strong, muscular, gizzard- 

 like stomach is supplied, at its terminal 

 portion, with the secretion of a great 

 number of long follicular glands. 



556. In the annexed figure of it 



(Fig. 199) the mouth is shown at a, a AJimentaiy canal, Aphroditaaculeata. 



