IN CYPRIS CINEREA. 243 



situated in a grazing meadow. PI. XVI., Fig. t, represents C. ci?ierea 

 somewhat crushed, to show these parasites or Cysticercooids in situ. 



It will be seen that they are situated in the dorsal region more 

 towards the posterior half of the creature, and over the intestine. 

 On opening or crushing the valves of Cypris in water, the 

 Cysticercooids float out in the liquid, but are held in check by a 

 long ribbon-like appendage (see Fig. 2, g.), whose end is attached 

 to the concavity of the shell of its host. It is seldom that these 

 parasites are solitary. Fig. i possesses two, which is the usual 

 number, but I have found as many as four inhabiting one Cypris. 



On being freed from its host, it has a great resemblance to 

 the head of an Echinococcus, Figs 2 and 3, with the anterior part 

 of the head invaginated, but a closer investigation soon dispels 

 this illusion, for although the circlet of hooks is similarly situated, 

 yet in point of structure they are totally dissimilar. 



The circlet of hooks is usually situated at the anterior part of 

 the Cysticercus in the medial line. 



The cuticle of the Cysticercus is striated or streaked, and at 

 various points in the striation it is fenestrated. Its structure is 

 harsh and firm, and resists the influence of boiling nitric-acid. 

 This cyst or capsule has nothing in common with the Cysticer- 

 cooid which it contains, beyond its protecting influence to prolong 

 the vitality of the embryonic head, until with its host it falls a prey 

 to some warm-blooded creature, in whose viscera it becomes a 

 perfect Tcenia scolex, but failing this it perishes with its host. 



The ribbon-like caudal appendage (Figs. 2 and 3) readily takes 

 picro-carmine stain and soon becomes disintegrated under the 

 influence of the nitric-acid test. It enters the cyst at the poste- 

 rior end, where there is a groove or slight depression. This 

 depression is the foramen or commencement of a short, circular 

 tube, which perforates the wall of the cyst and forms a stalk in the 

 interior, the end of the embryo resting on or being attached to it. 

 The ectoderm of this appendage enters the cyst through the 

 hollow stalk or tube, and then spreads itself out and forms the 

 investing membrane of the embryonic head. This membrane is 

 an integral part of the embryonic head, as at the anterior part of 

 the cyst it too becomes invaginated, the developing head being, as 

 it were, suspended in the cyst within this membrane. The approx- 



