30 W. BALDWIN SPENCEli. 



which surround the opening of the mid into the hind gut a 

 few cells evidently similar in structure to the typical gland- 

 cells of the body (fig. 59, Al. gl.). They have no ducts. There 

 do not appear to be any special gland-cells connected with the 

 oesophagus such as Stiles describes and figures in P. probos- 

 cideum, though in this region the parietal, hook-, and head- 

 glands merge into one another, and hence gland-cells lie, but 

 in no regular arrangement, around the oesophagus and pharynx 



(fig. 33, Pa. ^/.)- 



(4) There now remains a special structure, of the nature of 

 which I have not found it possible to speak with certainty. 

 This structure has the form of a somewhat irregularly shaped 

 mass of cells, which lies in the mid-dorsal line immediately 

 above the very anterior end of the mid-gut (figs. 10, 27, Gl.?). 

 The cells composing it are small ("025 mm.), and stand out in 

 striking contrast to the large gland-cells immediately around 

 them. There is apparently no duct connected with them, but 

 they are constantly present, and can be detected in every 

 specimen when sections are cut. They resemble much in 

 appearance the masses of small cells figured by Stiles^ as 

 surrounding the structures lying within the body-cavity in 

 a young female P. proboscideum. 



Functions of the Gland-Structures. 



We have under this head to deal with two sets of structures, 

 which are evidently, as before stated, very distinct from one 

 another, and have different functions to perform. P. tereti- 

 usculum feeds exclusively upon the blood which it obtains 

 directly from the walls of the lung of the snake in which it 

 lives. This blood it can only obtain by piercing the walls of 

 the delicate blood-vessels and by subsequent suction. To 

 effect these two processes special structures are present. For 

 the piercing of the walls, the oral papilla and tooth-like 

 structure in the posterior wall of the pharynx are amply 

 sufficient, owing to their capability of movement by muscles. 



' Loc. cit., Taf. viii, fig. 47. 



