Cuvierian System of Zoology, 105 



envelope. The nervous system is composed of many distinct 

 masses, united by nervous threads, the principal of these are 

 placed near the oesophagus, and have received the name of 

 the brain. In animals of this division we can only distinguish 

 the organs of two senses, which are those of taste and sight. 

 One single family only exhibits organs of hearing. The sys- 

 tem of circulation is, however, complete, and there are parti- 

 cular organs for respiration. The organs of digestion and 

 secretion are nearly as complicated as those of vertebrated 

 animals. 



The animals of this second form are called Molluscous 

 Animals {Animdlia mollusca). Although the plan of their 

 organisation, with respect to the external configuration of the 

 parts, may not be so uniform as that of vertebrated animals, 

 there is always a resemblance between these parts, at least of 

 the same degree, in the structure and in the functions. The 

 cuttle-fish, and animals with univalve or bivalve shells, belong 

 to this division. 



The third form is that which is observed in insects, worms, 

 &c. In animals of this division the nervous system consists of 

 two long chords, ranging along the belly, and swelling out at 

 intervals into ganglions or knots. The first of these knots, 

 placed near the oesophagus, is called the brain ; it is but little 

 larger than the rest. The envelope of the trunk is divided 

 by transverse folds into a certain number of rings, the cover- 

 ings of which are sometimes hard, and sometimes soft, but 

 the muscles are always attached to them beneath. The trunk 

 has often articulated members, or legs, on each side, but is 

 frequently without them. The animals of this form we call 

 Articulated Animals [Animdlia artiaddta). 



In the animals of this division we first observe the pas-^ 

 sage from circulation in a vascular system to nutrition by 

 imbibition, and a corresponding passage from respiration in 

 circumscribed organs to that in air-vessels called tracheae, 

 which are spread over the whole body. The organs of taste 

 and sight are the most distinct in the animals belonging to this 

 division ; one single family, only, exhibits organs of hearing. 

 The jaws are always lateral. 



The fourth form, which comprises all the animals known 

 under the name of zoophytes, may be called Radiated Ani- 

 mals [Animdlia radidta). 



In all the preceding divisions the organs of sense and mo- 

 tion are placed symmetrically, on the two sides of an axis; 

 in the animals of this fourth division they are placed circu- 

 larly, round a centre. Many radiated animals approach in 

 substance to the homogeneity of plants, they exhibit no dis- 

 tinct nervous system, nor organs of the particular senses ; in 



