THE CYSTIC ENTOZOA. 487 



IV. OF SPHAIRIDION.* (PLATE VI., FlG. 16.) 



Sphairidion acephalocystis is an animal allied to Acephalo- 

 cystis, chiefly from its acephalic character, but also from its 

 reproductive organ being enclosed within the centre of its sac. 

 This reproductive body or membrane is exactly similar to 

 the pedicle of the Cysticercus, with the exception of its being 

 entirely buried in the body of the animal, consequently also 

 it is neither furnished with teeth nor suckers. There is no 

 separate absorbent apparatus in the sac of the animal, and 

 this part of its body appears to be composed of one membrane 

 only, which is analogous to the external membrane of the 

 sac of Acephalocystis. The cyst of this animal at first 

 appears to be composed of three membranes, but a little 

 examination proves the outermost to consist of peritoneum 

 only, the two others being similar to the analogous membranes 

 of the cyst of Cysticercus rattus, namely, an external for 

 defence, and an internal for absorption of nourishment. 



This animal was found attached to the intestines of the 

 Balearic Crested Crane (Balearica pavonia, Vigors) beneath 

 the peritoneum. 



V. OF C^ENUEUS.f (PLATES VI, XII.) 



The next animal we have to describe is Caenurus. It is 

 in the species belonging to this genus that the first vestiges 

 of extremities are perceived, to which form of* structure we 

 are ]ed through Diskostoma the discs described in the latter 

 being without doubt analogous to the pedicles of the 

 Caenurus. 



Ccenurus cercbralis, an animal frequently found in the 

 brain of the sheep and other ruminants, has been long known 



* 2<f)ai.pi5iov, a globule. 



t Transaction* of the Royal Society, Edinburgh, vol. xv. p. 564. 



