Relation of Higher Animals to Man 545 



the wise" (176: 19). And this was the summing up also 

 reached by the writer on review of the apparent main Hne of 

 zoological progress (p. 503). 



It will generally be conceded that a highly evolved animal 

 economy would be one in which the skin or environally irrit- 

 able system, the protective or defensive system, the skeletal or 

 strengthening system, the muscular or motor system, the ali- 

 mentary or digestive system, the respiratory or aerating system, 

 the nervous or sensory correlating system, and the reproduc- 

 tive system are all sufficiently evolved and balanced as to ensure 

 ample perpetuation and continued steady evolution of the 

 species alongside destructive agents — either inorganic or or- 

 ganic. In a sentence it might be said that the ensuring of 

 continued and even progressive synthesis in the midst of agents 

 that might promote analysis represents true biological success. 



Viewed from such a standpoint it can be said that at least 

 five pronounced lines of evolutionary advance can be traced, 

 that have branched off from the main line. Each of them, 

 while showing sedentary or even degenerate species, contains 

 others that have advanced to a high degree of specialization. 

 These five in the apparent order of time and of evolutionary 

 complexity are: the Cephalopoda, the higher Arachnida, the 

 higher insects, the higher birds, and the higher mammals that 

 are inferior to man. When therefore in this chapter we use 

 the term "higher," we refer to those of the above five groups 

 that have decidedly evolved along highest lines beyond the 

 average of their kith and kin, and greatly higher than those of 

 their kith and kin that have become degraded. 



We incline much to add a sixth probably less important 

 group, the, Crustacea, did we know more, and more minutely, 

 of their sense responses and modes of life. For the present we 

 place it aside. 



Now when one compares all of these with man, and with an 

 average type of each group, it becomes evident that the most 

 important somatic system is the nervous, since alike in its com- 

 plex molecular substance and in its functional connections it 

 is the governing and correlating system. Spencer, Darwin, 



18 



