ON PEVELOT.MKXT ETC. OF TJIOROXTS. •>'>■> 



retractor musflcs in the collar cavity (fig>:. lo, 14, !•"), ret.) pro- 

 diicing at the same time a deep depression just in front of the 

 ganglion. It is also of almost constant occurrence that the gan- 

 glion is withdrawn inwards on the application of reagents, so as 

 to produce a shallow pit or groove in front of, or helow, the 

 ganglion (figs. Go r^ f/L). A cpiite similar fact is always ohserved 

 in Lovén's larva. From these circumstances T am much inclined 

 to regard the " neui'opore " of Mastermax not as a I'cally exist- 

 ing structure, Init as an artefact. 



As to the tentacles, I have at present nothing to add to what 

 is already known about them. 



o. Organs of Entohladh- OrUjhi. 



In the fully grown larv;e the alimentary canal is a long and 

 straiirht tuhe ; it begins with the mouth which is overliung bv the 

 preoral lobe, and ends at the anus in the centre of the anal cone 

 sin-rounded by the perianal belt (figs. 12-10). Of the whole ali- 

 mentary tract three parts may Ije distinguished : the Oesophagus, 

 the Stomach, and the Intestine. 



Oesophagus. In the eml)ryological part of this article I have 

 said that the oesophagus of Actinotrocha is of ectol)lastic origin, 

 so that the original gastrula mouth is to be sought at the jnnc- 

 tnre of the œsophagus with the stomach. The resophagus (Figs. 

 45, 48, and 49, œs.) is a comparatively short and narrow canal 

 with a wall composed of densely ciliated cylindrical cells, among 

 which are scattered numerous unicellular glands [m.gl.). Thus 

 the wall does not differ in structure from that of the hood or of 

 the collar. 



]\Iastermax lias described an unpaired ectodermal invagina- 



