68 CONTRIBUTIONS TO AMERICAN HELMINTHOLOGY. 



The measurements on Fig. 12 are taken from a specimen in which 

 the eggs are nearly ripe. The worm somewhat resembles a hammer 

 in shape, the body forming the shaft of the hammer and the tail- 

 piece the head. This resemblance is greater in the hardly-mature 

 specimens, where the oviduct is not dilated with eggs, and the body 

 consequently more linear in outline. 



The caudal lamina is considerably wider than the body. It is 

 longest at each side, and somewhat shorter in the middle through the 

 presence of a posterior notch, which may become considerably deeper, 

 dividing the disc into two very well marked halves when the large 

 caudal hooks are in vigorous action, owing to the course of the 

 mxiscular bands which are attached especially to the innermost forks 

 of these. The suckers resemble in all respects those of Polystomum ; 

 the prominent rims do not present the rounded apertures which I 

 have noticed above in P. oblongum. The diameter of the suckers 

 is 0.27 mm. The large hooks (Fig. 13) differ in form from those of 

 Polystomum or of any species of Dactylogyrus ; and, in fact, except 

 for the impair trabecula present in the latter genus, the hooks of some 

 forms of Dactylogyrus and of Polystomum resemble each other more 

 closely than they do those under consideration. The attached end of 

 the hook is divided into two pieces : one — the longer — a thin, flat, 

 somewhat linear splint in the continuation of the axis of the rounded 

 body of the hook; the other, thicker, shorter and rounder, standing 

 at an angle of 45° from that axis, with two prominences for muscular 

 attachment. T observe that the splint-iike portion is bent in some 

 specimens; this is perhaps due to pressure in mounting. The free 

 portion of the hook, just in front of the bend, bears two little curved 

 teeth, one rising from the surface of the other, which probably assist 

 in securing the attachment of the animal. Similar teeth seem to be 

 present on the hooks of Dactylogyrus monenteron, Wagener. ^^ 



I have not been able to elucidate very successfully the structure of 

 the smaller hooks. I have only attempted to indicate their position 

 in Fig. 12. Even their number remains somewhat doubtful; only 

 in one small specimen have I succeeded in making out sixteen. 

 They are much less easy to observe in the larger worms; perhaps 

 their functional importance diminishes with age, as I am inclined to 

 believe of the corresponding structures in Polystomum. Especially 

 those lying behind the large hooks seem to be important in the small 



27 Beitrage z. Enfcwick. d. Eingeweidewiirme, PI. XIII., Fig. 3. 



