110 MEMOIRS OF 



ticulated members on its sides, but is as often 

 without. These are the articulated animals, and 

 it is among them that we observe the passage of 

 the circulation in closed vessels, or nutrition by 

 imbibition, and the corresponding passage of 

 respiration in the circumscribed organs called 

 tracheae, or aerial vessels spread over the whole 

 of the body, by means of which it is performed. 

 Like the second form, there is but one family 

 which possesses t]ie organs of hearing, and those 

 of the taste and sight are chiefly developed. If 

 they have any jaws they are always lateral. The 

 fourth form embraces all the animals known 

 under the name of zoophytes, and is called that 

 of radiated animals. In all the preceding, the 

 organs of movement, and the senses, are sym- 

 metrically disposed on the two sides of an axis ; 

 they have a posterior, and an anterior face of 

 dissimilar appearance. But in those now men- 

 tioned, they are as if composed of rays round a 

 centre, even when there are but two series of 

 these rays, for then the two faces are alike. 

 They approach the homogeneity of plants : 

 they have no very distinct nervous system, nor 

 particular organs for the senses. In some there 

 are scarcely any vestiges of circulation ; their 

 respiratory organs are almost always on the 



