OF ANIMALCULES. 13 



this latter class, however, does not fall within the pro- 

 vince of this work. 



In the variety of systems that have been put forth 

 respecting these extraordinary creatures, the main cha- 

 racteristics of each have referred either to a difference 

 in their size, or to the general appearance of their ex- 

 ternal forms ; the present design, however, is not to 

 investigate the value of these. Until the introduc- 

 tion of vegetable colouring matter into the fluid, which 

 supplies them with food, — an experiment that has 

 been attended with very successful results, — these crea- 

 tures were commonly supposed to be entirely devoid of 

 internal organization, and to be nourished by the simple 

 process of cuticular absorption. By the application of 

 coloured substances, which, moreover, have been found 

 to invigorate rather than to depress the animalcule, and 

 to maintain it in the full exercise of all its functions, this 

 erroneous notion is set at rest, and an internal structure 

 is discerned in some, equal, if not surpassing that of 

 many of the larger invertebrated animals, and com- 

 prising a muscular, nervous, and, in all probability, vas- 

 cular system ; all wonderfully contrived for the per- 

 formance of their respective ofliices. 



The most obvious portion of their internal structure is 

 undoubtedly that connected with the digestive functions ; 

 and hence it is that Ehrenberg has selected this as the 

 leading feature of his arrangement, denominating his 

 two grand divisions of the Phytozoa, Polygastrica and 

 Rotatoria ; the former of which includes such as are pos- 



