THE CYSTIC ENTOZOA. 493 



cystis, as well as the reproductive and absorbing nucleus of 

 Sphairidion. 



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, etc. 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 

 similar to these of Cysticercus ; we have examples of this 

 occurring in the Nematoidea, Cestoidea, and Acanthacephala, 

 etc. As examples of the worms alluded to, I may instance 

 Trichina spimlis, 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 ex- 

 ample, too, of these peculiar forms, may be mentioned, a very 

 interesting animal which will be afterwards described, namely, 

 Neuronaia Monroii. 



The cysts of all these worms have similar structures to 

 those of Cysticercus, namely, an external membrane composed 

 of compressed cellular texture, and an internal membrane con- 

 taining 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 thickening and hardening of the external membrane of the 

 cyst, preventing 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 infested with Trichina, it is found on examination, that with 



