188 Prof. J. D. Dana on Cephalisation. 



2. By the anterior of the locomotive organs participating to 

 some extent in cephalic functions. 



3. By increased abbreviation, concentration, compactness, and 

 perfection of structure, in the parts and organs of the anterior 

 portion of the body. 



4. By increased abbreviation, condensation, and perfection of 

 structure, in the posterior, or gastric and caudal, portion of the 

 body : as, in the greater compactness and larger number of seg- 

 ments combined in the sacrum of the higher Megasthenes than in 

 that of Cetaceans or Edentates ; the less posterior elongation of 

 the vertebral column and body in the higher Megasthenes than in 

 Cetaceans, or in the tailless Batrachians than in the tailed species 

 of the group, &c. 



5. By an upward rise in the cephalic end of the nervous sys- 

 tem. This rise reaches its extreme limit in Man. Birds thus 

 show their superiority to Reptiles, but not to Mammals ; for the 

 Bird-type, like the Reptilian, is relatively diminutive in life- 

 system (infra, p. 196) ; its relation to the Reptilian type is 

 much like that of Insects to the Crustacean (p, 193). 



A decline in the grade of cephalization is shown by the re- 

 verse of these conditions : as (1) by a transfer of members from 

 the cephalic to the locomotive series; (2) by the posterior ce- 

 phalic organs participating in locomotive functions ; (3, 4) by 

 increased laxness, length and breadth, or spacing, among the 

 parts of either the anterior or posterior portion of the body, or, 

 further, a resolution, more or less complete, of the system of 

 structure into its equal normal elements or elementary parts ; 

 (5) by increased proneness in the position of the nervous system : 

 also — 



6. By an adaptation of the organs of the senses to locomotive 

 or prehensile purposes, — as in the case of the proboscis of the 

 Elephant, which is a perverted nose ; also the prehensile termi- 

 nations of the second antennse of many inferior Crustaceans. 



7. By an abnormal multiplication of the parts in the anterior 

 portion of the body, — as in the excessive number of teeth in 

 some Cetaceans and Edentates. 



8. By an abnormal multiplication of the parts in the posterior 

 portion of the body, — as in the abnormal multiplication of mem- 

 bers and segments in Phyllopod Crustaceans, Myriapods, &c. 



9. By a further degradation of the structure before and be- 

 hind, or a degeneration or obsolescence of the parts or organs, — 

 as in the absence of teeth in some Cetaceans and Edentates ; the 

 degradation of feet into fins, as in Whales, or their total absence; 

 the absence of a series of abdominal members in Entomostracans; 

 the absence of antennae in Articulates, provided the senses corre- 

 sponding to these organs are absent or comparatively imperfect; 



