660 INFUSORIA. 



idea. But, even in the present limited state of our information, this department of 

 nature is a very extensive one, and requires the study of a whole lifetime to obtain even 

 a moderate knov.'ledge of all its branches.] 



The greater part of the Infusoria have a gelatinous body, and a very simple organ- 

 ization ; but some naturalists have included among them other animals, which are far 

 more complex in their organization, and which agree with them only in the smallness 

 of their size, and the habitats in which they are usually found ; — these will constitute 

 our first order ; but we must retain the doubts, which are not yet cleared up, respecting 

 their organization. 



THE FIRST ORDER OF THE INFUSORIA. 



ROTIFERA. 



These are, as we have stated, distinguished by a more complicated organization. Their body 

 is of an oval shape, and gelatinous , and we can observe that they have a mouth, a stomach, 

 an intestine, and a vent near the foot. The body usually terminates in a sort of tail, variously 

 formed ; and it has on the fore part a very singular organ, variously divided into tubes with 

 toothed edges, the teeth of which vibrate in various ways, and give the organ the appearance 

 of one or more toothed wheels, revolving with greater or less rapidity. The apparently revolving 

 organ does not appear to convey food to the mouth ; and so it may be, in some way, con- 

 nected with the function of respiration. 



FURCULARIA, — 



Or the Rotifera properly so called, have the body unarmed, and the tail composed of articulated portions, 

 which enter into each other. 



Trichocerca, have the rotatory organs a little less developed. Vaginales, are said to resemble the fonner, 

 inclosed in a transparent membrane ; but that is doubtful. 



Tubicolaria, form for themselves little habitations of foreign substances, out of which the rotatory organs are 

 protruded, in a manner similartothetentacula of polypi. Branchionus, are distinguished by a sort of membranous 

 shield on the back. 



THE SECOND ORDER OF THE INFUSORIA. 



HOMOGENEA. 



The body of these shows no viscera, or other complex organization, and in many there is 

 not even a vestige of a mouth. 



The first tribe comprehends those which, with a gelatinous body, more or less contractile in several 

 parts, has yet cilise, or some other simple external organs. 



Urcolaria, have the shape of a horn, but with ciliae. Trichoda, have a flat body, ciliated at one extremity. 

 Leucophora, have ciliae all round the body. Kerona, have the cilise like little horns. Hiantopa, have them 

 prolonged in a sort of threads. 



The second tribe have no external organ, except a tail. 



Cercarea, have an oval body, with a thread-like termination. The seminal animalculae, which have given 

 occasion to so many whimsical hypotheses, belong to this genus. 



Vibrio, have the body round, like a very minute bit of thread. The " Eels in paste and in vinegar," as they are 

 called, belong to this genus. 



EnchcUs, have the body oblong, more soft, and less defined than that of Vibrio. ITiere are various other forms. 



Proteus, are so constantly changing their shape, that no definition or description of it can be given. 



Monas, are, even under the microscope, mere points, which move with great rapidity, though they have no appa- 

 rent organs of motion. 



Volvo.v, are globular bodies, revolving on their axes, and containing more minute globes, each of which also, in 

 all probability, contains a numerous embryo race. 



