168 



ACTINOZOA. 



is equally sceptical . On the other hand, the careful 



Milne 



and, more 



recently, of Gegenbaur, point to an opposite con- 

 clusion. Somewhat similar are the views of Frev 

 and Leuckart. All the preceding writers are un- 

 animous in rejecting the prior account of the 

 nervous system of P leurobrachia given by Grant 

 who describes a double nervous ring surrounding 

 the mouth, in the course of which he thought he 

 could detect eight ganglia, each giving off on 

 either side two fibres and a fifth larger filament 

 traceable onwards beyond the middle of the body 

 Yet this description, when carefully considered, is 

 less irreconcileable with the views expressed 'on 

 the same subject by other observers than seems to 

 be usually supposed. 



Certain curious appendages, which possess, per- 

 haps, a tactile function, have been observed by 

 R. Wagener in two genera of Ctenopkora, Beroe 

 and Pleurobrachia. These organs appear as long 

 hair-like threads, which arise from either side of 

 the ctenophores along their whole length, and 

 form around each pole of the body a sort of 

 wreath, composed of several concentric rings. The 

 threads have not been seen to exhibit anv inde- 

 pendent movements. Each swells once or twice 

 in the course of its length into a smooth or angular, 

 rounded or flattened, expansion, the entire surface 

 of which is abundantly beset with minute stalked 

 knobs. In some threads smaller swellings, want- 

 ing the capitate stalks, take the place of those 

 just noticed. Occasionally the threads branch 

 and, instead of ending in points, terminate in 

 dilatations of a like nature to those which inter- 

 rupt their filiform axes. 



