Gradation of ilie Vertebrata. 141 



artificial. Gradation being thus a judgment must liave its 

 basis. Wlietlier it has been distinctly recognized or not, the 

 same one has been instinctively and universally adopted, viz : 

 power, physical and psychological, qualitatively as well as 

 qiiantitatively considered. This is made prominent in Prof. 

 Dana's articles on " Cephalization as a Basis of Classification," 

 and is a clearly recognized ground- work of his ideas, so far as 

 they are gradational in their nature. Most writers, while con- 

 sciously or unconsciously recognizing the basis, have looked 

 to the principle of "division of labor" for a decision. While 

 this is an important element of power, it is not the sum total 

 nor any sure indication of it. But the point I wish to make 

 in this connection is this, power is by no means all physical. 

 Intellectual and moral forces cannot be ignored. A gradation 

 that does not recoscnize these is as false as a classification based 

 exclusively upon them. Now the nervous system is the 

 especial instrument of mental manifestation. Its forms indi- 

 cate, so far as they can be interpreted, the mental characteris- 

 tics. Are we not compelled then to seek in its forms, and in 

 its developments, that natural co-ordination of mental and 

 physical indices of rank which alone can form a rational basis 

 of gradation ? That the systems commonly relied upon do 

 not give us the truth approximately and in a general way is 

 by no means asserted. The general truth of their results is 

 assumed, and is made the basis of what arguments are here 

 presented. 



The following are suggested as indicative points : 



l-s^. Position of the general line of the cerebrospinal axis. 



This is essentially horizontal in fish, acknowledged to be the 

 lowest of the vertebrates ; perpendicular in man, the highest ; 

 intermediate in a general sense in the intermediate orders. 

 These facts have been fi'equently noted and appealed to as 

 indicating rank. Some difficulties in application and sources 

 of error exist, owing to modifications due to habits of life and 



