252 Description of the Plates. 



its spines and suckers^ is developed; whilst out of the thickened 

 disc the deeper layers of the cortex are formed. Each head thus 

 at first points inwards towards the interior of the parent cyst ; but 

 by the contractions of the muscular layers of this cyst, as also by 

 those of the intrinsic muscles of the cortex of each head, it may 

 come to have its apex pointing- in either direction, either outwards 

 towards the circumambient tissues of its host, or inwards towards 

 the interior of the maternal vesicle. 



a. Wall of embryonic dilated cyst, containing, as do the homo- 



logous structures in the other Platyelminthes, calcareous 

 corpuscles. 



b. Hooks of embryonic vesicle scattered and dislocated by its 



distension. 



c I. Scolex fully protruded. 



c 3. Scolex half protruded. 



cl. Scolex as developed with its apex pointing inwards and its 

 tubular body in communication therefore, not with the 

 parent cyst, but with the cavity of the adventitious cyst 

 thrown round the entire organism by the irritated tissues 

 of its host. The central parenchymatous portion of none 

 of these scolices is as yet developed, the sexual organs of 

 which the central parenchyma is all but exclusively made 

 up, not being developed except in the cestoid stage attained 

 to in the intestine of the dog. 



For history of Caenurus cereiralis, see Van Beneden, L c, p. 146 ; 

 Cobbold, Entozoa, p. 1 1 6 seqq, ; Gamgee, Report on the Para- 

 sitic Diseases of Quadrupeds used as Food (Med. Officers' 

 Privy Council Office Report, v. 1862) ; Thudichen, ibid., vii., 

 1865. 



For other figures illustrating the various stages in the development 

 of these Taeniadae, see Cobbold's Entozoa, p. 116, pi. xii., et 

 passim. 



