Recent ResearcJies on tfie Infusoria. 297 



^^^^^ Af, General coverings of the body. ^ ^^^^^^^ ^^^ ^.^ 



The body, in many infusoria, is naked ; in others it is jwo- 

 tected by a covering or lorica, of which there are several varie- 

 ties, differing from each other in form and substance. Some- 

 times it resembles the shell of a tortoise, surrounding the animal 

 completely in the middle, with an opening before and behind, 

 through which the head and tail project. This form is named 

 a testa or shell. In other cases, it covers only the back of the 

 animal, being open below ; it is then named scutellum, Tho 

 urceolus is a covering or case, shaped like a bell or like a cylin- 

 der closed at one end, within which the animal can withdraw it^ 

 self at will. The lacerna, or mantle, is a very curious provi- 

 sion. It is a sort of dense gelatinous covering, which would 

 seem to be formed out of the most external layer of the animal's 

 body. Within it the substance of the animal separates into several 

 young ones, which are for a time enclosed, but at length escape 

 by the bursting of the envelope (Fig, 1^.) The parent animal 

 would therefore seem to lose its individual existence, and to be 

 at length converted into a mere capsule, containing the young. 

 This form is found in Volvox, Eudorina, Pandorina, and 

 Gonimrt. Lastly, the covering sometimes consists of two pieces, 

 when it is named Lorica hivalvis. 



B. Exterior divisions of the body. 



In the greater number of infusoria, the body presents a pretty 

 obvious division into heg^l, trunk, and tail. There is seldom 

 any well-marked indication of a neck. 



The head is very obvious in the Rotatoria, it is that part of 

 the body which bears the rotatory organs and the eyes. Within 

 it are contained the large cerebral ganglions, the cavity of the 

 mouth, and masticating apparatus. The limit between the head 

 and trunk, which is sometimes marked by a slight constriction, 

 is named the nucha, or nape of the neck ; its position is further 

 marked by the attachment of the nervous loop to the skin, and 

 often more conspicuously by an eye here situated. In the Po- 

 lygastric Infusoria, the head is seldom capable of being pointed 

 out as a distinct part. 



The trunk is well defined in those infusoria which possess a 



