32 



ORGANS OF SUPPORT^ 



the serpuke exude a calcareous conical tube from the surface 

 of their skin, which enlarges like the conical shell of a gas- 

 teropod, by the successive addition of new and wider cones 

 to its interior surface. But the true skeleton of these arti- 

 culated worms, as in the higher entomoid classes, is their 

 exterior skin and epidermic covering, to which the muscles 

 of locomotion are attached, whether this part be hard or 

 soft. The upper lateral setae of the annelides appear to be 

 the analogues of the wings of insects, and other corresponding 

 parts extending from the sides of the segments in higher 

 classes. When the setae of the annelides are hollow and 

 jointed, or sub-articulate, they are commoiily called cirrhi, 

 as we see in the long jointed cirrhi accompanying the tufts 

 of setae on the sides of the nereides. One of the most 

 articulated forms of the body and members presented by 

 this class is seen in the sea-centiped, the nereis nuntia, re- 

 presented in Fig. 14, where a dorsal view of the entire ani- 

 mal is given at 1, a transverse section of a single segment at 

 2, and a magnified view of one of the lateral organs of mo- 

 tion at 3. We already find in this worm FIG . 14. 

 the head (Fig. 14. l,a, b) distinct from the 

 trunk, and consisting of several separate and 

 moveable segments. The head is provided 

 with sharp, curved pointed maxillae, with ser- 

 rated inner edges. There are numerous se- 

 parate small simple eyes, or ocelli, disposed 

 chiefly in transverse rows, and there are se- 

 veral lateral tentacular filaments having the 

 character of antennae. There is an enlarged 

 anterior part of the trunk (Fig. 14, 1, b, e,) 

 corresponding with the thorax of insects, 

 and the segments are nearly equally develop- 

 ed from this point to the posterior end of 

 the trunk. All the segments of the head 

 and trunk are still moveable on each other ; 

 they are almost equally developed and equally 

 provided with lateral appendices. In the 

 transverse view of one of the segments (Fig. 

 14, 2,) of this nereis, we observe the lateral 

 appendices to consist, on each side, of a long 

 jointed slender tubular cirrhus (Fig. 14, c, d,) and a fasciculus 



