478 



ANNELIDA. 



342) appears to consist of short conical segments, the broad ends 

 of which are turned away from the mouth of the tube. Though 

 the general aspect of the tubes of Conchicolites is very similar to 

 that of Cornulites, the micro-structure of the tube is very different 

 in the two genera. In Contulites, as has been shown, the tube has 

 a characteristic vesicular structure (fig. 335, c). On the other 

 hand, thin sections of the tube of Conchicolites (fig. 335, d) show 

 it to be devoid of this cellular structure, and to be composed of 

 imbricating calcareous plates, which are fibrous in character, and 

 which overlap in such a way that the broad upper ends of the 

 successive rings are directed towards the interior of the tube. 



Sub-order II. Errantia. — The Polychaetous Annelides in- 

 cluded in this sub-order are free-living animals which do not form 

 for themselves investing-tubes. The body is usually elongated, 

 each segment carrying on its sides tufts of horny setae, attached to 



Fig- 343- — a, Head of Nereis incerta, viewed from beneath, and enlarged (after Quatrefages) : 

 d, The principal pair of chitinous jaws (the dark dots on the lobe behind these are smaller den- 

 ticles) ; pa! , Internal pair of palpi ; pa, External or greater pair of palpi ; 1 1 1, Tentacles. B, 

 Foot-tubercle of Nereis, enlarged: no, Notopodium ; ne, Neuropodium ; c, Dorsal cirrhus; d ', 

 Ventral cirrhus ; b b b, Branchial filaments ; a, Aciculse ; j s, Setae attached to the dorsal and 

 ventral oars. 



fleshy, double tubercles or "parapodia" (fig. 343, b). The mouth 

 is furnished with horny or partially calcified jaws (fig. 343, a). The 

 branchiae are attached to the sides of the body, or to the dorsal 

 surface. Though the integument of the Errant Annelides secretes 

 chitinous matter to a certain extent, a resistant exoskeleton is not 

 developed, the only hard structures present being the chitinous 

 setae and the horny jaws, the lower pair of the latter (and sometimes 

 the upper pair also) being more or less completely calcified. Owing 

 to the soft nature of their integument and foot-tubercles, it can only 

 be under the most favourable conditions that the actual body of an 

 Errant Annelide can be preserved in the fossil state. Specimens 



