404 GYMNORHYNCHUS HORRIDUS. 



entozoon, is the manner in which it is enclosed in a firm and 

 close cyst. It appears to me that this cyst is not altogether 

 the result of irritation of the surrounding tissues. The outer 

 coat of the cyst may be of this nature, but it is not so easy 

 to conceive the inner tunic to be due to the same cause. Pro- 

 fessor Owen, in his memoir on the Trichina spiralis — the 

 entozoon of the human muscles — holds that the cyst of that 

 animal, although apparently consisting of two tunics, is the 

 result of irritation. Dr. Knox, again, considers it to be a part 

 of the animal, although the latter lies free in the cavity. This 

 latter opinion is inadmissible, according to the usual con- 

 ception of an individual animal. Might we not conceive the 

 cysts to be essential parts of all such entozoa, inasmuch as 

 they are never absent? and may we not suppose them to be 

 parts of the original ovum within which the animal was 

 formed, and in which it passes the term of its existence? 

 Without having any facts to adduce in proof, I hazard this 

 supposition as a hint for future research ; and as it is not at 

 variance with any of the known conditions of animal existence, 

 it is worth consideration in a fresh investigation of the subject. 



