THK r.H.Y.'ILETA. 207 



the anterior region of the bdy. Tii.-y very generally have a 

 prohoscis, provided with chitinnns trrth. 



The singular genus, Tomopteri*, i- i tian-p.-in-tit pelagic 

 Annelid, with numerous parapodia, eacli terminated by two 

 lobes representing the neuropodium and n a- -podium, hut 

 with setee, two of which are very long, only in the cephalic 

 region. 



The sedentary Annelids (Tubicola) fabricate tubes, either 

 by gluing together particles of sand and shells, or by secret- 

 ing a chitinous or calcified shelly substance, in which tii.-y 

 remain (e. g., Protula, Fig. 54). The praestomium is small or 

 wanting ; none have a proboscis ; there are no cirri ; and the 

 parapodia are short or rudimentary, The branchiae are d- 

 oped only on the anterior somites, and the latter are ot'tni 

 markedly different from those which constitute the posterior 

 part of the body. 



In some (Serpulidce) a tentacle is enlarged and its end 

 socretes a shelly plate which serves as an operculum, and 

 shuts down over the mouth of the calcareous tube inhabited 

 by the animal, when it is retracted. The dilated end of the 

 opercular tentacle sometimes serves as a chamber in which 

 the young undergo their development (species of Spirorbix). 



The alimentary canal of the polychseton '-fit raivly 



presents any marked distinction between stomach and intes- 

 tine, and is almost always of the same length as the body, ex- 

 tending, without folds or convolutions, from its anterior to 

 its posterior extremity ; but in Siphonostomum ( Chlora , 

 Pectinaria and others, it is more or less convoluted. It is 

 attached by membranous bands, or more complete mesenteries, 

 to the walls of each somite, and very commonly pr dila- 



tation between every pair of mesenteries. In most Potycf* 

 the intestine acquires in this way merely a moniliform appear- 

 ance, but in Polynoe^ Aphrodite, Sigalion, and their allies, 

 long creca are given off upon each side of the alimentary 

 canal, and, sometimes becoming more or less convoluted, ter- 

 minate at the upper part of each segment (Fig. 51, />) < 

 beneath, or in the branching where such orga: 



The anterior portion of the alimentarv canal is, in a [ 

 number of the Polychceta, in fact in all the typical / 

 so modified as to constitute a distinct muscular pharynx, the 

 anterior portion of the wall of which can be everted like the 

 finger of a glove, from the aperture of the mouth, and the 

 posterior portion protruded, so as to form a proboscis. In 

 Polynoe squamata, the proboscis is one-fourth as long as the 



