OF WORMS 



951 



plume of which is replaced by a single long bristle-like appendage 

 that is in continual motion, its point moving round and round in a 

 circle. This curious organism, first noticed by Johannes Miiller, has 

 been since ascertained to be the larva of some species of the Nemer- 

 tine worms, which belong to the division Anopla, a group in which 

 there are no stylets to the proboscis. 1 



Among the animals captured by the tow-net the marine 

 zoologist will not be unlikely to meet with a worm which, 



FIG. IVl.Pilidium gyrans . A, young, showing at a the alimentary 

 canal, and at b the rudiment of the Nemertid ; B, more advanced 

 stage of the same ; C, newly freed Nemertid. 



although by no means microscopic in its dimensions, is an admirable 

 subject for microscopic observation, owing to the extreme trans- 

 parence of its entire body, which is such as to render it difficult to 

 be distinguished when swimming in a glass jar except by a very 

 favourable light. This is the Tomopteris, so named from the 

 division of the lateral portions of its body into a succession of wing- 

 like segments (fig. 718, B), each of them carrying at its extremity a 

 pair of pinnules, by the movements of which it is rapidly propelled 

 through the water. The full-grown animal, which measures nearly 



1 See especially Leuckart and Pagenstecher's ' Untersuchungen tiber niedere 

 Seethiere ' in Miiller's Archiv, 1853, p. 569 ; and Balfour, op. cit. p. 165. The Author 

 has frequently met with Pilidium in Lamlash Bay. 



