190 Introduction to Animal Morplwlogy. 



trical (Sipunculus), or alternate (Phascolosoma). In 

 Sipunculus, some filaments unite with the circular 

 muscular fibres. Eye-specks are present in a few 

 adults, and the larva of Sipunculus has four, close to 

 the ganglion, but vanishing in development. The front 

 of the body in some is prolonged into a proboscis, usu- 

 ally retractile by means of two or four muscular bands 

 from the body wall, and ciliated, often armed with 

 bristles, and sometimes surrounded by tentacles. The 

 mouth is terminal or slightly ventral (Sternaspis), and 

 the pharynx is armed in Priapulidae with horny teeth. 

 Salivary caeca open herein in Sipunculus (Kef cr stein 

 and Ehlers}. The intestinal canal is ciliated within 

 anil without; small in calibre; slung by mesenteric 

 thn-ads; ran-ly by a nu-mbrane; it may be scarcely 

 Ion in T than the body (P. brevicaudus) ; or more 

 usually, long and coiled. (In an Echiurus of 6" it 

 nicasun-d 3!'.) Its middle region is glandular, often 

 \.-llo\vish (hepatic r), as in Bonellia ; or with numerous 

 glandular caeca appended (Phascolosoma). The oral, 

 gastric, and intestinal regions are distinguishable 

 in the young, sometimes in the adult (Priapuli 

 The anus may be dorsal, sometimes anterior, even 

 at the junction of the body and proboscis, or ter- 

 minal. 



There may be no vascular system, or it may con- 

 sist of two long vessels, one along tfre medio-ventral 

 line, giving off many branches to the intestine and the 

 wall of the body, and one dorsal running along the 

 intestine, and often coiled with it. 



In Sipunculus these are joined by a circumoral vessel, 

 which sends prolongations into the hollow tentacles, and has 

 appended to it one or two contractile sacs like the Polian 



