ITS ZOOLOGICAL IMPORTANCE. 155 



wards. Therefore a classification, to be true and natural, 

 must accord with the succession of organs in the embryonic 

 development. This coincidence, while it corroborates the 

 anatomical principles of Cuvier's classification of the Animal 

 Kingdom, furnishes us with new proof that there is a general 

 plan displayed in every kind of development. 



323. Combining these two points of view, that of Embry- 

 ology with that of Anatomy, the four divisions of the Animal 

 Kingdom may be represented by the four figures which are 

 to be found, at the centre of the diagram, at the beginning 

 of the volume. 



324. The type of Vertebrates, having two cavities, one 

 above the other, the former destined to receive the nervous 

 system, and the latter, which is of a larger size, for the intes- 

 tines, is represented by a double crescent united at the cen- 

 tre, and closing above, as well as below. 



325. The type of Articulata, having but one cavity, grow- 

 ing from below upwards,^and the nervous system forming 

 a series of ganglions, placed below the intestine, is repre- 

 sented by a single crescent, with the horns directed up- 

 wards. 



326. The type of Mollusks having also but one cavity, the 

 nervous system being a simple ring around the oesophagus, 

 with ganglions above and below, from which threads go off 

 to all parts, is represented by a single crescent with the 

 horns turned downwards. 



327. Finally, the type of Radiata, the radiating form of 

 which is seen even in the youngest individuals, is represented 

 by a star. 



