28 W. BALDWIN SPENCEE. 



The cells form an irregular mass of no definite shape^ which 

 from about the level of the oesophagus (or in the male of the 

 genital opening) passes forwards occupying the spaces inter- 

 vening between the strongly developed muscles of the head 

 region. The consequence is that there is no body-cavity in 

 the head region, and that the latter is comparatively solid ; so 

 that, apart from their excretory function, the cells of the head- 

 gland must be of considerable use in forming a firm support 

 for the body-wall in this region, where are present the most 

 important muscles, the efficient working of which depends 

 upon their having a firm insertion. Stiles and Hoyle describe 

 the continuity of these cells with those of the glands described 

 above as hook-glands, Hoyle giving to them no special name, 

 whilst Stiles restricts to them the name of hook- glands in con- 

 sequence of their having in P. proboscideum a special rela- 

 tionship to ducts opening beside the hooks. This special rela- 

 tionship does not obtain in P. teretiusculum, though at the 

 same time they probably pour their secretion partly into the 

 duct opening on the primary papillae, and partly into those 

 opening by the side of the hooks. 



Ducts of the Hook- and Head -glands. — Lohrmann 

 described the ducts of the head-glands as opening on two 

 prominent papillae on the head. Stiles, in P. proboscideum, 

 states that the ducts of the head-gland (= hook-gland as de- 

 scribed above) open ventrally to the papillae, whilst those of 

 the hook-glands (= head-glands as described above) open in 

 relation to the hooks. Leuckart has described the hook- 

 glands (= those described above under the same name) as 

 opening in relation to the hooks, and in the case of P. oxy- 

 cephalum states that the duct passes through the nerve-ring — 

 a relationship which has not, I think, been observed in any 

 other form. In P. teretiusculum the ducts are arranged 

 as follows : — In the hook-gland of each side there is for the 

 posterior two thirds of its course a single main duct. Anteriorly 

 this, on each side of the body, breaks up into three branches 

 (figs. 6 and 7, a, 6, c) ; of these three one passes to each hook of 

 its own side, and one— the largest — runs on through the head 



