124 EMBRYOLOGY. 



classes, orders, and families, such as the heart, the respiratory 

 apparatus, and the jaws, are not distinctly formed until after- 

 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 Ani- 

 mal Kingdom, furnishes us with a 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 and 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 be- 

 ginning 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 

 intestines, is represented by a double crescent united at the 

 centre, and closing above, as well as below. 



325. The type of Articulata, having but one cavity, and 

 growing from below upwards, (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 threads going off from it, is represented by a single 

 crescent with the horns turned down. 



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

 which is seen even in the youngest individuals, is repre- 

 sented by a star. 



