456 



ZOOLOGY 



SECT. 



.iruboscis, which is the greatly produced prostomium ; in Bonellia 

 (Fig. 356) the proboscis, when fully extended, is five or six times 

 the length of the body : in Echiurus (Fig. 357) it is much shorter : 

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

 the mouth. In Priapidus (Fig 358) there is at the posterior end 

 an elongated simple or bifurcated caudal appendage covered with 

 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 



-prob 



ard set 



FIG. 356. Bonellia yiridis. Entire 

 animal (female) with the proboscis 

 moderately extended. (After Greef.) 



posr.set 



FIG. 357. Echiurus, entire animal. 

 A lit. set. anterior setze ; post.stt. pos- 

 terior setae ; prob. proboscis. (After 

 Greef.) 



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, 

 sometimes with oblique and internal circular layers superadded. 

 There is an extensive undivided coelome, covered, as in the case of 



