94 THE ANATOMY AND DEVELOPEMENT 



as well as the reproductive and absorbing nucleus of Sphairi- 

 dion. t 



Species of Cysticercus have been found in almost every part 

 and cavity of the human body. In the brain, eye, lungs, liver, 

 in the walls of the intestines, and in the muscles. In the present 

 state of our knowledge, it is impossible to say how these animals 

 gain such habitats as the eye, &c. This is a question, however, 

 which has been the cause of much discussion. 



VII. OF THE HIGHER CYSTIC ENTOZOA. 



Besides those already described, there are many other forms of 

 entozoa of the higher orders, which are inhabitants of cysts simi- 

 lar to these of Cysticercus ; we have examples of this occurring in 

 the Nematoidea, Cestoidea, and Aeanthacephala, &c. As exam- 

 ples of the worms alluded to, I may instance Trichina spiralix, 

 Gymnorliynchus horridus, and a small filaria inhabiting the livers 

 of some fish, but, as far as can be made out, not hitherto described 

 by any author. As another example, too, of these peculiar forms, 

 may be mentioned, a very interesting animal which will be after- 

 wards described, namely, Neuronaia Monroii. 



The cysts of all these worms have similar structures to those 

 of Cysticercus, namely, an external membrane composed of com- 

 pressed cellular texture, and an internal membrane containing 

 absorbing cells, through which the contained animal obtains 

 nourishment. 



In the descriptions of the acephalocysts already given, it will 

 be remembered how the animal died in consequence of the thick- 

 ening and hardening of the external membrane of the cyst, pre- 

 venting the absorption of nourishment from or through it ; so in 

 like manner do these higher Cystic Entozoa Trichina die 

 from a similar cause. In many cases where the subject is in- 

 fested with Trichina, it is found on examination, that with few 

 exceptions almost every specimen is converted into the hard cre- 

 taceous matter spoken of, many, at the same time, presenting all 

 the intermediate stages of decay. Gymnorhynchus presents us 

 with a very curious habit dependant upon this mode of structure, 



