Monadina.] THE INFUSORIA. 91 



the Monas guttula, hyalina, gliscens, Okenii, and socialis ; 

 or longitudinally, as with the Monas punctum (see figure 2) ; 

 both methods have been observed with the vivipara. The 

 formation of gemmules has not been perceived in this genus. 



Ehrenberg supposes that they are endowed with the 

 faculty of sensation, and that this is shewn by the vibration 

 of the proboscis, and its alternate quiescence when the 

 creature is in a place abundantly supplied with food. In 

 some of the species an eye-like organ has been discerned, 

 but as the species of each genus should be reduced to the 

 rule of a special organ, characterizing a particular genus, 

 these are not considered as true Monads, but form distinct 

 genera, as Microglena, &c. 



As the Infusoria of this genus are chiefly curious on 

 account of their extreme minuteness, and in no other 

 respect, the species are not deemed of sufficient interest 

 to be expatiated upon at any great length ; their leading 

 characters and size, therefore, are only given. And we 

 may remark, generally, that most of them are inhabitants 

 of water in which any organic matter is undergoing 

 decomposition. 



The Monads are arranged under two divisions, according 

 to their external forms. The first division contains all 

 those which are of a globular or oval shape (globular 

 Monads), and the second those of a lengthened form, 

 more than twice as long as broad (elongated Monads). 



A. GLOBULAR MONADS. 



(a). True Globular or Sphero-Monad colourless or whitish. 



1. MONAS crepusculum. The twilight Monad. The 



animalcules of this species are the smallest of all living 



creatures. They are of a spheroidal form and hyaline, 



