CLASSIFICATION. 381 



more or less close external resemblance." This conception 

 survived until the time of Cuvier. " Naturalists," says Agas- 

 siz, " were bent upon establishing one c'ontinual uniform 

 series to embrace all animals, between the links of which it 

 was supposed there were no unequal intervals. The watch- 

 word of their school was : Natura non facit saltum. They 

 called their system la chaine des 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. 

 CI. 1. Mammalia. 

 CI. 2. Birds. 

 CI. 3. Reptilia. 

 CI. 4. Fishes. 



Second Branch. ANIMALIA MOLLUSCA. 

 CI. 1. Cephalapoda. 

 CI. 2. Pteropoda. 

 CI. 3. Gasteropoda. 

 CI. 4. Acephala. 

 CI. 5. Brachiopoda. 

 CI. 6. Cirrhopoda. 



Third Branch. ANIMALIA ARTICULATA. 



CI. 1. Annelides. 

 CI. 2. Crustacea. 

 CI. 3. Arachnides. 

 CI. 4. Insects. 



Foui-th Branch. ANIMALIA RADIATA. 

 CI. 1. Echinoderms. 

 CI. 2. Intestinal Worms. 

 CI. 3. Acalepha3. 

 CI. 4. Polypi. 

 CI. 5. Infusoria. 



