204 



ZOOLOGY. 



near the mouth. The umbrella is gradually withdrawn into 

 the mouth, so that eventually only a crown of short tooth- 

 like projections surrounds the mouth. Finally the whole 

 umbrella is swallowed, the arms at the end of the body dis- 

 appearing, while the end of the intestine projects far out 

 from the body behind the mouth. By this time the Plioro- 

 nis form is clearly indicated, the body being long and slen- 

 der and the mouth surrounded by a crown of short tentacles, 

 the end of the intestine being entirely withdrawn within the 

 body. These changes are rapidly effected. The larva of 

 Echiurus is formed on the Annelid type. 



In PJiascolosoma cceinentarium (Quatrefages), the body is 

 much shorter than in P. Goul- 

 dii ; the worm lives in compara- 

 tively deep water (10 to 50 fath- 

 oms), in dead, deserted shells, 

 building out the aperture by a 

 conical tube of sand. In Sipun- 

 culus (Syrinx) the tentacles are 

 fringed or lobed. It does not 

 occur in American waters. 



In Echiurus the intestine ends 

 at the end of the body, and there 

 is a circle of bristles at the pos- 

 terior end, while Bonellia differs 

 in having an enormous proboscis, 

 and only a few bristles near the 

 head. In Bonellia viridis Eol. 

 of the Mediterranean (Fig. 141), 

 the proboscis is deeply forked ; 

 the intestine is very long, convo- 

 luted, and into the cloaca empty 

 two excretory organs. The ovary 

 is a cord-like organ, which in the 

 posterior part of the body is fast- 

 ened to the intestine. 



ChcBtoderma nitidulum Lov6n 



off the coast of Europe and 



The body is long, cylindrical, and 



f„^l 



Pig. ii\.— Bonellia viridis ; 

 profescis coiled several times. 

 fore end of the proboscis ; s, s', 

 row in the proboscis ; i, i, digestive 

 canal ; m, mesenterial threads (only 

 shown on the anterior end of the di- 

 gestive canal); g, organs of excre- 

 tion : c, cloaca ; «, oviduo* — After 

 Lacaze-Duthiers ; from Gegenbaur. 



occurs in 20-40 fathoms 

 Northern Nev.' England, 



