PHYLUM ANNULATA 



40Y 



t < ntacles, or by a lobod and plaited tentacular fold. The prostoniium 

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

 introvert, bat 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 



ant set 



Fie. 390.— Bonellia viridis, entire 

 animal (female) with the proboscis 

 moderately extended. (After Grecf.) 



pQ5t.Set 



Fie. 301.— Echiurus, entire animal. 

 ant. set. anterior seta.' ; post. set. pos- 

 terior setaj ; 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 multicellular) 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, 



VOL I K K 



