IN CYPRIS CINEREA. 247 



extreme length is about the twelve-hundredth of an inch. The 

 points of the hooks are, on the evaginated rostrum, turned towards 

 the posterior end of the creature. 



From an expression of Leuckart's, I learn that the question of 

 these cysts containing fluid is a controvertible point, and I can 

 only express my regret that I am unable to substantiate my asser- 

 tion from specimens in my possession, having failed to arrest the 

 emission of the fluid for mounting purposes ; but I may quote an 

 authority who, like myself, has watched the emission of this fluid, 

 viz.- — Mr. Pugin Thornton, M.R.C.S., of this city. Although I 

 have taken C. cmerea and other species of the Cypridce from ponds 

 in this neighbourhood and the surrounding districts, embracing a 

 radius of ten miles, yet none of them have been the host of this 

 Cysticercus, and it is only in this one particular pond that they are 

 parasitic in the Cypris. How the pond has become affected is a 

 point which requires solution ; neither can I find any record of 

 the knowledge of their existence as parasites in these minute 

 crustaceans. 





EXPLANATION OF PLATES XVL, XVII. 



Fig. 1. — Cijpris cinerea, crushed to show Cysticercooids in situ, x 50, 

 2. — Cysticermis, with ribbon-like caudal appendage, x 155. 

 3. — Same, x 350 : — a, fenestration ; 6, epithelium of cyst ; 



c, fluid cavity ; d, investing membrane of embryonic head ; 



e, rudimentary head ; /, short, circular tube ; g, ribbon-like 



caudal appendage. 

 4, 5, 6. — Cysticercooids in different stages of progression, under 



the influence of nitric acid, x 150 : — a, papillar ; b, same 



further developed ; c, circlet of hooks ; d, dome of rostrum ; 



e, thread-like muscle-fibres ; /, investing membrane of 



embryonic head. 

 7. — Head of developed Cysticercooid, x 350: — a, suckers; 



6, rostrum inverted ; c, circlet of hooks. 

 8. — Head of same flattened to show the suckers and circlet of 



hooks, Zeiss, |-in. D.D. 

 9. — Rostrum, hooks, and suckers, x 350. 

 10.— Hook of same, x 1,080. 



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