64 A FURTHER KNOWLEDGE OF THE CYSTIC CESTODES, 



do SO widen out to become inserted into it. They, like the similar 

 longitudinal fibres in the Cysticercus from Hoplocephalus, probably 

 have to do with the invagination of the head. 



In histological structure the Cysticercus under consideration 

 agrees closely with the Cysticercus from Hoplocephalus, in which 

 1 have gone into detail more fully. Below the cuticle the outer 

 circular and inner longitudinal layers of elastic fibres can be 

 recognised, and internal to these the subcuticula, consisting of a 

 richly nucleated layer of radially elongated cells, whose outlines, 

 however, owing to the small size of the Cysticercus, are difficult 

 to make out. 



The ground tissue is composed of a matrix with scattered nuclei, 

 but here, as distinguished from the Hoplocephalus Cysticercus, the 

 posterior part is solid, there being no indication of a central cavity. 

 In this respect it agrees with two forms mentioned by Leuckarb,* 

 "one from the sub-epidermal tissue of the nightingale and another 

 from the body cavity of Lacerta vivipara ( Piestocystis Dithyridium, 

 Diesing)," in which no bladder cavity is present. 



As to the development of the Cysticerci, the material at my 

 disposal did not offer any certain developmental stages, but it 

 seems probable that the Cysticerci arise by a process of prolifera- 

 tion from the thin inner lining of the cyst cavity, which, together 

 with the cellular network in the interior of the cyst, I interpret 

 as the direct derivative of the six-hooked embryo, representing 

 the blastogen of Villot. The small mass of cells attached to the 

 lining of the cyst in Fig. 8 probably represents the first stage in 

 development of one of the Cysticerci, This bud probably increases 

 in size, becomes separated from the wall, and conies to lie free in 

 the cavity of the cyst, forming a mass of cells such as are seen in 

 the right hand corner of the cyst cavity in Fig. 8. Later, round 

 this mass the cuticle is differentiated, and finally by an invagina- 

 tion at one end the head is developed, the suckers developing on 

 the interior of the invagination cavity, 



* " Parasites of Man," p. 343. 



