14 GENERAL HISTORY OF 



shell -less, or illoricated Infusoria, whilst the latter denotes 

 the loricated. I shall, therefore, adopt the terms loricated 

 and illoricated in this work, because they appear to be the 

 least objectionable ; for, although, in etymological strict- 

 ness, lorica simply means a shell, yet, as we commonly 

 attach the idea of a certain composition to the word shell, 

 it may be as well to avoid the use of it, for the following 

 reasons : — 



The Lorica differs greatly as to its composition in 

 different species. In some cases it is composed entirely of 

 silica ; in others, of lime, with a portion of the oxide of 

 iron. In some, it is combustible; in others, not so. 

 There is a difference also as to the proportion of envelope- 

 ment of the creature within the lorica. Some Infusoria 

 are entirely encased, as in a box or pitcher ; whilst others 

 are only so in part, having merely a shield or carapace over 

 them. In the latter, the covering resembles that of the 

 Chilonia or turtle tribe. 



As, in very minute genera, it is often difficult to ascer- 

 tain, by a mere inspection, whether they are enclosed 

 within a lorica or not, it will not be deemed uninteresting 

 to point out the manner in which this may be determined. 

 Having obtained some specimens of the Infusoria, we will 

 suppose of the family Cryptomonas {figs. 21 to 33), place a 

 drop of water containing them in an aquatic live-box, 

 compressor, or crush-box, mixing a little colouring matter 

 with the water, according to the directions given in the 

 section '* On feeding Animalcules tvith coloured Mate- 

 rials," when, if loricated, a clear transparent ring will be 

 observed, encircling the animalcules, and keeping them 

 separate from the fluid in which they are immersed : — 



