ON A NKW HI.STRIORDEIJilD. 327 



segments. In Dinopliilus there is sometimes (D. meta- 

 meroides) an undivided post-anal or tail region, beset with 

 small adhesive papillae, with glands serving as organs of 

 attachment. In both groups the ventral nervous system 

 consists of metamerically arranged ganglia, though in 

 Dinophilus there are two separate chains connected by trans- 

 verse commissures (at least in Schimkewitsch's species) into 

 a ladder- like structure (25). Dinophilus wants the tentacles 

 and cirri ; possesses bands or a cavity of cilia, and a pair of 

 eyes. In some species the metameric condition of the 

 nephridial system is more pronounced than in the Histriob- 

 dellidas. in others less so ; there is an extension forwards into 

 the head. In Schimkewitsch's species there are metameric- 

 ally arranged bundles of annular muscular fibres, and a pair 

 of ventral longitudinal muscles. In the alimentary canal 

 there is a close resemblance between the two groups, though 

 the horny jaws are absent in Dinophilus. Though Dino- 

 philus possesses a mesoderm, segmented in the larval condi- 

 tion, developed from primitive mesoderm cells, its general 

 body-cavity has no epithelial lining, and the equivalent of 

 the coelom is reduced to the cavity of the reproductive 

 organs. In the reproductive organs there is a considerable 

 similarity between the two groups, especially in respect of 

 the male apparatus with its median penis and associated 

 hypodermic mode of impregnation, and the paired vesiculae 

 seminales. 



On the whole I consider that there is more reason for 

 including Dinophilus and the Histriobdellidse in one class 

 than for grouping either of them with the Polygordiid^e. 



It is obviously of radical importance in connection with 

 this question to determine if those features of the Histriob- 

 dellidse which seem to be of a primitive nature can be 

 explained as a result of degeneration. If the Histriob- 

 dellida3 ai-e degenerate they must be degenerate Chsetopods, 

 or, at all events, degenerate achaetous Annelids. If we are 

 to take this view, we must at the same time acknowledge 

 that, side by side with the supposed degeneration, there must 



VOL. 43, PART 2. NEW SKRIES. Z 



