ox DEVELOPMENT ETC. OF PTTOIÎOXTS. 570 



represented in lig. 11. It is no doiil)t tlirown off together with 

 the other parts of tlie preoral lol)e. Besides, it is equally true 

 that the epistonie can not he found in the neighhourhood of the 

 larval mouth at such a stage, while, on the other hand, in the 

 worm after metamorphosis the rudimentary organ is seen as a 

 small bud on the dorsal median margin of the mouth. 



As before noted, the ring nerve of the adult is not yet formed 

 in the swimming larva. This nerve and the so-called brain of the 

 adult are of new formation ; and the complicated nervous system 

 which had developed only in the ])reor;d lobe, suffers the same 

 degeneration as that larval organ. In fig. i'A c the ring nerve 

 ivm.Y'' is seen in section, just exterior to the se])tum {mf>^.). It 

 consists of a thick lavei- of very fine nerve fibres. 



IV. Supplementary Notes. 



J. MÏTLLEE ('46), the first discoverer of Adinolrorlia, des- 

 cribed the animal as an adult worm under the name Actinotroclia 

 JirancJiiala. The ventral pouch was considered by him to be the 

 sexuid organ. Doubts were afterwards thrown on his views by 

 Krohn ('54) ; and they were finally refuted by Schneider ('62), 

 who maintained that Acl'tiiotrocha is the larval form of a certain 

 Gephyrea. This idea was confirmed by Kowalewsky ('67) who 

 ascertained that Actinotrocha is the free swimming laiva of 

 P/ioronis. Since this renowned discovery of Kowalewsky nu- 

 merous papers on the anatomy and development of Fhoronis have 

 been published by uiany celebrated naturalists. But the singular 

 fact is that the life history of the animal has not been sul)jected 



" Unhappily the letter y is misprinted in the phite as v. 



