604 STRUCTURE AND DEVELOPMENT OF THE ECHINOCOCCUS-HEADS. 



anterior half by a more granular parenchyma (striated only in the 

 interior), and by a greater accumulation of calcareous corpuscles. 

 The calcareous corpuscles are somewhat large, or at any rate no 

 smaller than in the other cystic bladder-worms, but their numbers are 

 extremely variable in different specimens. On treatment with acids 

 they exhibit a brisk fermentation. 



In favourable objects one can distinguish four coiled longitudinal 

 vessels, which unite in pairs before their entrance into the stalk, and 

 are connected below the circlet of hooks by means of a ring-like 

 anastomosis. Here and there are also some rapidly moving ciliated 

 lappets. Otherwise the parenchyma of the body is upon the whole but 

 little differentiated, and the musculature of the suckers in particular 

 is much less distinctly defined than is usually the case in other cystic 

 bladder-worms. 



As to the hooks, it is well-known that they are distinguished from 

 those of the adult Tcenia (see Fig. 315) by the short and slender form 

 of their roots, especially in the case of the larger ones. It sometimes 

 appears as though the basal portion were wanting, as is indeed really 

 the case (p. 582). This imperfect development of the roots affects 

 the size of the hooks, as is shown by the fact that three linear 

 measurements taken from hooks of the first order amounted to 03, 

 0'015, and 0'014 mm. respectively, and three taken from those of the 

 second order 0'024, 0'013, and 0'014 mm. The first line extends from 

 the point of the hook to the end of the posterior root, the second from 

 the same point to the end of the anterior one, while the tliird indicates 

 the distance between the ends of the two roots. 



In spite of the solid nature of the head, the anterior half, with the 

 circlet of hooks and suckers, may be entirely invaginated into the 

 posterior portion. In this state the head has an almost spherical 

 shape (018 mm.), like a Vorticella, with retracted 

 circlet of cilia. In the middle of its free anterior 

 border there is a more or less large depression, which 

 marks the place where the invagination has taken 

 place. Below this one sees the suckers, and further 

 down, in the neighbourhood of the stalk, the circlet 

 of hooks is observed shining through the paren- 

 chyma. The points of the hooks are, as a rule, 

 FIG. 323. Echino- directed upwards and outwards, so that, in its 

 the retracted state, the anterior part of the head has 

 head invaginated. ( x exactly the position and relation to the enclosing 

 posterior portion, which we saw the Cysticercus-lieaA 

 to bear to its so-called " caudal bladder." Nevertheless it is impossible 

 to regard the capsular envelope of the retracted JZckinococcus-head as 



