BY J. P. HILL. 79 



the inturning of a cushion-like thickening of the bottom of the 

 invagination sac into its interior. Concerning the further develop- 

 ment of the plug he says : "An diesem Zapfen spielen sich die 

 weitereu Veiiinderungen ab, an ihm bilden sich die Saugnapfe 

 und der Hakenkranz." 



The matter is well summed up by Villot* : " La verity est que 

 la tete des Cystiques peut se d^velopper de deux manieres bien 

 differentes," and we can now extend Villot's view to the Tetra- 

 rhynchidce. 



Returning now to the scolex-forming bud in Synhothrium, at 

 the stage under consideration the bud is typically knob-shaped, 

 being attached to the bottom of the involution sac by a narrow 

 stalk, which widens out into an expanded and rounded head. It 

 consists of a fairly compact mass of small rounded cells, such a 

 tissue among the Cestodes having, according to Moniez,t all the 

 characters of cells in process of reproduction. In the anterior 

 broader portion of the bud there are large clear spaces, and the 

 small cells are not so numerous ; in the stalk the tissue is of a 

 denser character, the cells being more numerous and larger. In 

 the anterior region are seen two denser areas radiating outwards. 

 These are in all probability the fundaments of the proboscides. 

 Below the cuticle of the blastocyst at this stage an external layer 

 of circular fibres and an internal layer of longitudinal fibres can 

 be recognised ; then internal to these is the granular layer con- 

 taining nuclei lying at some distance from each other ; the cell 

 boundaries are not distinct. 



Fig. 17 is a longitudinal section of the next stage I have been 

 able to obtain. It is separated by a somewhat wide interval from 

 the preceding stage, for the knob-shaped process has not only 

 given rise by elongation to the external form of the adult scolex, 

 but internal differentiation lias advanced to a considerable extent. 

 The cyst, of which Fig. 17 is a longitudinal section, had a length 

 of only 3-5 mm., so that the size of the cyst is evidently not 



* Cystiques des T^nias, p. 20. 

 + Loc. cit. p. 37. 



