THE FOUR CLASSES 1303 



The third form is that remarked in worms, insects, 

 etc. Their nervous system consists of two long cords, 

 running longitudinally through the abdomen, with 

 which they communicate by filaments that encircle 

 the aesophagus like a necklace. The covering or 

 envelope of the body is divided by transverse folds 

 into a certain number of rings whose teguments are 

 sometimes soft, and sometimes hard; the muscles, 

 however, being always situated internally. Articu- 

 lated limbs are frequently attached to the trunk; but 

 very often there are none. We will call these ani- 

 mals Animalia Articulata, or articulated animals, 

 in which is observed the transition from the circula- 

 tion in closed vessels to nutrition by imbibition, and 

 the corresponding one of respiration in circum- 

 scribed organs, to that effected by tracheae or air- 

 vessels distributed throughout the body. In them 

 the organs of taste and sight are the most distinct; 

 one single family alone presenting that of hearing. 

 Their jaws, when they have any, are always lateral. 



The fourth form, which embraces all those ani- 

 mals known by the name of zoophytes, may also be 

 properly denominated Animalia Radiata, or radiated 

 animals. We have seen that the organs of sense and 

 motion in all the preceding ones are symmetrically 

 arranged on the two sides of an axis. There is a 

 posterior and anterior dissimilar face. In this last 

 division they are disposed by rays round a centre; and 

 this is the case even when they consist of but two 

 series, for then the two faces are similar. They ap- 

 proximate to the homogeneity of plants, having no 

 very distinct nervous system or particular organs of 



B VOL. IV. 



