512 ON TWO REMARKABLE SPOROCYSTS, 



The mantle-folds and the visceral mass in the region between the 

 adductor muscles had the appearance of being provided with a 

 ramifying system of vessels containing a blood-red fluid. These 

 apparent vessels, when examined under the microscope, were 

 found to be narrow ramifying Sporocysts, the germinal epithelium 

 of which contained a red colouring matter apparently identical 

 with that occurring in the SjDorocyst described in the first part 

 of this paper. "^ In these Sporocysts were mature Cercarise and all 

 stages in their development. The Cercari?e proved to belong to 

 the remarkable form known as Buceiji]ialus^ v. Baer, the larva of 

 G aster ostomum. All of these are developed in narrow, tubular, 

 usually branching Sporocysts; but in no case hitherto recorded, 

 so far as I am aware, is a red colouring matter present. 



The Cercarise (fig. 32) are relatively small, being only 0*25 mm. 

 in length when fully matured. They are sluggish in their move- 

 ments, and the tail was never observed to be used as a swimming 

 appendage, its only movements being slow^ waving ones, or such 

 as resulted in each of the branches being coiled into a spiral and 

 uncoiled again. Such spiral movements were noticed by v. Baer 

 in Bucephalus p)oIyinorphus. It seems likely that the tail is used 

 more for attachment than as an organ of active locomotion. 



The body is long and narrow. The anterior portion, lodging the 

 anterior sucker or proboscis, is separated off from the rest by a slight 

 constriction. Its anterior end (figs. 33-36) varies in appearance 

 according to its condition. When somewhat contracted it usually 

 appears trilobed; when it is more extended the rounded aperture 

 of the sucker appears at its extremity. The anterior extremity 

 is beset with excessively minute cuticular spinules which gradually 

 decrease in size as they pass backwards, and are no longer distin- 

 guishable when the middle of the body is reached. A pair of 

 relatively long and slender cilia, presumabl}" sensory, extend 

 forwards from the extreme anterior end. 



* The nature of this coloaring matter has not yet been investigated. Its 

 spectum does not shew the absorption bands characteristic of that of haemo- 

 globin. 



