21 
give rise to an anomaly (fig. 8) first described by Blanchard (1886f), 
and also noticed b}^ Grassi & Calandruccio (1887a). 
Rostellum . — Besides suckers the head possesses another organ of 
attachment, namely a protractile and freel}^ movable rostellum (figs. 
6, 7, 9-15), armed with hooks. In preserved material the rostellum 
is usually found retracted, but in material which has been fixed while 
still living, or in the live worm itself, is often seen extruded. 
A B 
]8 
Krabbe, 1865, pi. .3, figs. 56-57.) B. Same from mouse (ifws mMsc■M7^^s). Enlarged. (After Krabbe, 
1865, pi. 3, figs. 58-59.) 
Fig. 17. — Hook of II. nana. Enlarged. (After Leuckart, 1886a, p. 996, fig. 409B.) 
Fig. 18. — Hooks, of II. nana. A, from man; B. from the rat. (After Linstow, 1896a, figs, iii and 3.) 
Fig. 19. — Hook of II. nana. Enlarged. (After Railliet, 1893, p. 294, fig. 191.) 
Fig. 20. — Hooks of H. nana. Enlarged. (After Mertens, 1892, fig. 3) 
Fig. 21.— Hooks of H. nana. A, complete crown: B, isolated hooks. Enlarged. (After Krantz from 
Kiichenmeister & Ztirn, [?1881], pi. 5, fig. 4.) 
Hooks . — The hooks (figs. 16-21) are arranged in a single row around 
the anterior part of the protrusible portion of the rostellum. Their 
number seems to be rather variable, with a range, putting together 
the numerous recorded observations, of 20 to 30. Leuckart (1863) 
gives 22 to 21 and (1886a, p. 997) 21 to 28; Easch (1891) 22; Miura & 
Yamazaki (1897) 23; Zograf (1893) 23 to 28; Grassi & Calandruccio 
(1887a) 21 to 28; Linstow (1896a) 21; Moniez (1888), in eight specimens. 
