120 



DKSCRIPTTON OF 



A recent paper, published by M. Agassiz, makes us acquainted 

 with the views of that eminent natiiralist on the questio vexata of the 

 relations of the Infusoria to other organized beings. He observes, 

 *■' Recent investigations upon the so-called Anentera have satisfac- 

 toiily shewn, in my opinion, and in that of most competent observers, 

 that this ty^e of Ebrenberg's Pohjgo.strica without gastric cavities, 

 and without alimentary tube, are really plants belonging to the order 

 of Algae in the widest extension of this group, wliile most of the 

 Monas tribe are merely moveable germs of various kinds of other 

 Algae." (Ann. Nat. Hist. 1850. p. 156.) 



The above \T.ews opposed to the animal natiu'e of the Mbnadt'na 

 are given m extenso, but the candid observer will find, if he examines 

 these organisms, that the balance is in favour of theh' being animal. 

 The extreme minuteness of these animalcules renders it difficult for 

 the mind to comprehend them or compare them with large animals, 

 but difference of magnitude, however great, is no actual bar to -sdtal 

 power, while the cilia of the animalcule connects man himself with 

 it, the fia'st moving instrument in the human embrj-o being a cilium, 

 which is retained to the end of life. 



Genus Monas. — TJie Monads. — The animalcules of this genus — the 

 true Monads — are described (see Table) as being deficient of the eye, 

 projecting lip and tail, and always swimming in the direction of the 

 longitudinal axis of the body, their mouth being situated at the 

 anterior part. It is another distinguishing character of the true 

 Monad that it is never seen to cluster with others of its genus, so as 

 to form a berry-Hke mass, and hence it is designated single, in con- 

 tradistinction to aggregate. At present, there are twenty- six species 

 of this gemis known — two green, two yellowish, three inclining to 

 red, and the remainder coloiu'less ; but it should be mentioned, that 

 although there be colour, it must not be regarded as a characteristic 

 to be entirely relied upon. Monads may often be present in water, 

 under inspection, ^dthout being seen, tlxrough the want of a 

 competent magnifying power. They will be sought for in vain 

 with a power of less than 300 diameters, and even this, in some 

 cases, will be found insufficient. They are besides, as a genus, 

 difficult to be accurately determined, not only on account of their 

 exceeding minuteness, but because the young of animalcules of 



