i'lLAKlDiE. 69 



rounded by a variable number of papilla, head continuous with the 

 body, anus terminable or nearly so, tail of the male obtuse, bluntly 

 pointed or slightly expanded, penis consisting of a long spiculum, 

 which is often accompanied by a short accessory piece. These 

 characters will pretty well embrace all the genera I propose to 

 include in the Filaridae, but in the present stage of our knowledge 

 it becomes extremely difficult to offer an arrangement which shall 

 supersede the method adopted by Dujardin. Probably no author, 

 past or present, has enjoyed such a practical acquaintance with the 

 Nematodes as the late Professor at Eennes, and yet his mode 

 of classification is not generally accepted. In this family I 

 place Dujardin' s osculant genus Heligmus, which although it 

 displays a trilobate mouth is only furnished with a long solitary 

 spiculum ; and for similar reasons I also include in this family 

 Diesing's singular genus Peritrachelius, as weU as the genus 

 Stephmmrus, because the hexa-punctiform mouth of the latter and 

 its truncate tail in the male (furnished with a single spicule only) 

 will not permit its incorporation with the Ascarides proper. 



In accordance with the design and scope of the present work it 

 is not possible to do more than select a single genus to illustrate this 

 Nematode family, numerically great in genera, as I have here 

 represented it to be. The typical genus Filaria is, in itself, per- 

 haps, one of the least interesting of the genera considered struc- 

 turally, and therefore I select the closely allied genus Trichoce- 

 phalus, as sufficiently characteristic of the family under considera- 

 tion. Helminthologists have described some eight or ten different 

 species as belonging to this genus, the two most common, and by 

 their similarity of external characters liable to be confounded, being 

 the common whip- worm of man, and that of our domestic ruminants. 

 The former (Trichocephahis disparj wiU be separately noticed in the 

 second part of this work, and therefore the latter (T. affinisj, which 

 is a comparatively little known species, may now engage our 

 attention. 



To the naked eye Trichocephahts affinis does not differ materially 



