CLASSIFICATION. 299 



says Agassiz, "were bent upon establishing one continual 

 uniform series to embrace all animals, between tbe links of 

 which it was supposed there were no unequal intervals. 

 The watchword of their school was : Natura non facit 

 taltum. They called their system la chaine dcs etres" 



The classification of Cuvier, based on internal organization 

 instead of external appearance, was a great advance. He 

 asserted that there are four principal forms, or four general 

 plans, on which animals are constructed; and in pursuance 

 of this assertion, he drew out the following scheme. 



First Branch. ANIMALIA VERTEBRATA 

 CL. 1. MAMMALIA. 

 CL. 2. BIRDS. 

 CL. 3. REPTILIA. 

 CL. 4. FISHES. 



Second Branch. ANIMALIA MOLLUSCA. 

 CL. 1. CEPHALAPODA. 

 CL. 2. PTEROPODA. 

 CL. 3. GASTEROPODA. 

 CL. 4. ACEPHALA. 

 CL. 5. BRACHIOPODA. 

 CL. 6. CIRRHOPODA. 



Third Branch. ANIMALIA ARTICULATA. 

 CL. 1. ANNELIDES. 

 CL. 2. CRUSTACEA. 

 CL. 3. ARACHNIDES. 

 CL. 4. INSECTS. 



Fourth Branch. ANIMALIA RADIATA. 



CL. 1. ECHINODERMS. 



CL. 2. INTESTINAL WORMS. 

 CL. 3. ACALEPEUE. 

 CL. 4. POLYPI. 

 CL. 5. INFUSORIA. 



