70 



BNTOZOA. 



from tlie human species, but the anterior narrow or capUlary 

 portion is comparatively finer and longer. The male is readily 

 distinguishable from the female by its spirally incurved tail, 

 and this spiral is not precisely in the same direction or plane 

 as the general falciform curvature of the thick body of the 

 animal (Plate V., Fig. 1), but turns laterally and obhquely on one 

 side, so as to form a sort of conchoidal projection. This feature 

 was first remarked on and described by Mr. Erasmus Wilson,* and 

 I have endeavoured to represent the same character in the accom- 

 panying plate (Fig. 4). The male is further distinguished from the 

 female by its long spiculum, and also from the male of Tricocephalus 

 dispar by the comparatively much greater length of the sheath 

 surrounding the spicule ; moreover, the position of the reproductive 

 orifices in the two sexes is equally distinctive. "With a pocket 

 lens the surface of the worm appears smooth throughout ; but 

 when highly magnified, peculiar markings are seen on the anterior 

 thin portion or capillary neck. This part presents a tolerably uni- 

 form thickness along its entire course, measuring about the jI; 

 of an inch transversely, but at the finely-pointed head immedi- 

 ately below the mouth the diameter is about the ^ of an inch 

 only. In the fresh state, the head often appears lobed or 

 furnished with lateral appendages, the aspect of which is very 

 variable. Kuchenmeister has described the evanescent character of 

 similar structures surrounding the mouth in T. dispar, and he regards 

 these lobes as forming a peculiar organ, capable of eversion and 

 inversion, and not as the mere result of accidental sarcode-for- 

 mation. Mr. Erasmus Wilson, who has also noticed this structure, 

 speaks of it rather more definitely in the following terms : — "Im- 

 mediately below the point of the head," he says, " the integument 

 is raised from the surface beneath, and more or less distended, so 

 as to constitute a prominent transparent collar. In some of the 

 specimens this collar was absent, but in the greater number it 

 was present, either partially or completely expanded. Its purpose, 



* See " The Veterintiiy Eeoord aud Transactions." Vol. ii., p. 47. 1846. 



