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 
muscular 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. I observe that the splint-like 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. Entwick. d. Eingeweidewiirme, Pl. XIIL., Fig. 8. 
