BY J. P. HILL. 71 



which the blastogen (proscolex) gives rise by endogenous budding 

 to a single caudal Ijladder, as distinguished from the genus Poly- 

 cercus, in which, according to Villot, a number of caudal bladders 

 are similarly produced. 



Structure of Monocercus Didymogastris. — The Monocerci lie 

 embedded in the wall of the intestine, generally in the superficial 

 layers. They appear to the naked eye as small rounded elevations 

 of a whitish colour, which vary considerably in size, the largest 

 observed measuring -5 mm. in diameter and the smallest '18 mm. 

 Each (Fig. 12) consists of two very distinct parts: (1) An outer 

 clear cellidar portion which we may provisionally term the cyst, 

 and which surrounds (2) a central more opaque portion, the 

 Cysticercoid proper. Considering these two parts separately, and 

 first as to the outer portion. In section it is found externally 

 to consist of a homogeneous membrane apparently of a cuticular 

 nature and which stains more deeply than the cuticle of the 

 Cysticercoid. Internal to this cuticular membrane is a single 

 layer of large cells, each containing protoplasm with refractive 

 granules and a nucleus ; their walls are continuous with the outer 

 membrane and stain similarly to it. In the possession of this 

 well-defined surrounding layer of cells, in the fully developed 

 Cysticercoid, Monocercus Didymogastris appears to differ from all 

 previously described forms belonging to this type. In Cysticercus 

 arionis, Ijeuckart* describes the Cysticercoid as surrounded by a 

 true connective tissue cyst derived from the host. But Moniezf 

 says : — " Le kyste dans lequel est enferme le Cysticerque de 

 VArion est pour nous, un produit du parasite lui-meme et non une 

 secretion de I'hote." He, however, describes the cyst as consisting 

 of concentric layers, an observation which Villot shows, J from the 

 study of G. arionis and G. glomeridis, to be incorrect. According 

 to him — "Le soi-disant kyste des Monocerques est, en realitie, une 



* "The Parasites of Man," English Edition, p. 361. 

 t " Essai Monographique sur les Cysticerques, " Travaux de I'lnstitut 

 Zoologique de Lille, T. iii. fasc. 1, p. 74. 



J Loc. cit. p. 38. 



