PHYLUM ANNULATA 



497 



tentacles, or by a lobed and plaited tentacular fold. The prostomium 

 is in such forms quite rudimentary. In the Armata there is no 

 introvert, but an elongated, highly contractile, simple or bifurcated 

 proboscis, which is the greatly produced prostomium ; in Bonellia 

 (Fig. 390) the proboscis, when fully extended, is many times the 

 length of the body: in Echiurus (Fig. 391) it is much shorter: 

 at the base of the proboscis on the ventral side is the opening of 

 the mouth. In Priapulus (Fig. 392) there is at the posterior end 

 an elongated simple or bifurcated caudal appendage covered with 



-prvb 



FIG. 3UO. Bonellia viridis, entire 

 animal (female) with the proboscis 

 moderately extended. (After Greef.) 



FIG. 301. Echiurus, entire animal. 

 (mt. set. anterior seta? ; -post. set. pos- 

 terior seta? ; prob. proboscis. (After 

 Greef.) 



hollow papillae. The anus is situated at the posterior end of the 

 body in the Armata ; in the Inermia it lies far forwards on the dorsal 

 surface, except in the case of Priapulus, in which it is terminal. 



Body-wall.- -Beneath the cuticle is an epidermis, which, is com- 

 posed of a single layer of cells. Among the cells are unicellular 

 (rarely multi cellular) glands, and sensory cells. Various colouring 

 matters, such as the bright green characteristic of Bonellia, are 

 contained in the cells of the epidermis. The muscular wall of the 

 body consists of external circular and internal longitudinal layers, 



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