SECT. ir. INFUSORIA. 71 



able both in size and number. It was on account of 

 the digestive vacuoles that the Infusoria were called 

 Polygastria by Ehrenberg. 



Transparent contractile vesicles of a totally different 

 nature from the vacuoles are peculiarly characteristic of 

 such Infusoria as have a digestive cavity. They exist 

 either singly or in even numbers, from 2 to 16, according 

 to the species, and never change their places ; but they 

 dilate and contract rhythmically at pretty regular 

 intervals. When dilated, they are filled with a clear, 

 colourless fluid, the product of the digestive process 

 which they are supposed to diffuse through the body of 

 the animal. 



The Euglena, a very extensive genus of Infusoria, 

 have smooth bodies and green particles imbedded in the 

 sarcode, which fills their interior ; and M. Wohler dis- 

 covered that the green mantle covering the saline 

 springs at Rodenberg and Konigsborner, which consists 

 of three species of these green Infusoria, gives out bub- 

 bles of pure oxygen ; thus indicating a respiratory pro- 

 cess in these animals, the same with that in plants, 

 namely, fixing the carbonic acid of the atmosphere and 

 exhaling oxygen, a singularly close analogy, if not iden- 

 tity, of action. The Euglense are also distinguished by 

 an irregular oblong space in the head filled with a red 

 liquid ; but, as it does not contain a crystalline lens, it 

 can only be regarded as the very earliest rudiment of an 

 eye, totally incapable of distinguishing objects, though 

 probably sensible to the influence of light. They swim 

 with a smooth gliding and often rotatory motion, pro- 

 ducing a kind of flickering on the surface of the water 

 by the lashing of a long filament attached in front, and 

 supposed to be their only organ of locomotion ; never- 

 theless, Mr. Gosse thinks that they are covered with 

 most minute cilia from their manner of swimming. The 

 Euglena acus is one of the prettiest of these little 



