ZOOLOGY. 557 



Class 12. IVeurozoa, Otozoa. 



3386. Those Sarcozoa, whose nervous system is for 

 the first time perfectly developed, and whose ear is open 

 externally, are the Birds. 



3387. The completion of the nervous system is the 

 brain ; now the brain defines or determines the head ; 

 the Bird is, properly speaking, the first Encephalic 

 animal. 



3388. In the Bird the head has for the first time, and 

 that indeed suddenly, freed itself from the trunk, and 

 been placed upon a long neck, far removed from the 

 thorax. In no class are there such long necks and so 

 many cervical vertebrae to be found as in Birds. They 

 can be therefore called also Cervical animals, as the neck 

 is not simply present, in order to render the head in- 

 dependent or self-substantial. 



The caudal vertebrae, on the contrary, are lessened 

 throughout the Birds, to a degree met with in no other 

 class of animals. 



3389. The brain separates for the first time com- 

 pletely into cerebrum and cerebellum, begins to exhibit 

 convolutions, and has in general most of the individual 

 parts analogous to those in the Thricozoa. They are 

 therefore Encephalic animals, which the name of Neu- 

 rozoa will properly enough imply. The nerves are in 

 comparison with the spinal cord much thinner than in 

 Reptiles and Fishes. 



In the Bird also, all the spiritual or mental faculties 

 make their appearance for the first time and suddenly, 

 whereas in the preceding classes but slight traces of 

 them were observed. Such for example are their me- 

 chanical instincts, varied modes of nidification, powers of 

 imitation, susceptibility to instruction, knowledge of 

 their benefactors, sentiment of joy, wheedling or coaxing 

 manners, and so on. We have no example of Fishes and 

 Reptiles having learnt any artificial tricks. 



3390. Birds are the closest repetition of the Insects, 

 but stand remote from the Crabs and Acalephae, indica- 



