246 J. D. Dana—Cephalhization a fundamental principle 
an organ of great size and power and chief reliance in locomo- 
tion, to one of diminutive size, and no locomotive power; anda 
having their locomotive functions located in the posterior parts 
of the body ;* and that in the higher, the forces, or force-organs, 
are more and more forward in the structure. For example, 10 
the whale—the tail is the propelling organ and is of enormous 
power and magnitude, and the brain is very small and is situ: 
ated far from the head extremity in a great mass of flesh an 
bone furnished with poor organs of sense; a grade up, 10 the 
the head is shortened anteriorly or in the jaws and pies not 
mates thus toward the condition in man. ‘The existence © onl 
* The fact that fishes have, with few exceptions, the tail as eae ci ae 
locomotive organ, corresponds with their inferior position int cephalization ia 
At the same time, it makes the application of the principle of ce ps the 
determining grade among them quite difficult. In most classes of cong 
force-organs constitute a series along the body, and the position - ay But in 
and the transfer forward with the rise in grade, is openly of its 10c0T0- 
nearly all fishes, the tail the | tive organ, with no transfer LMS og 
tive function to more anterior members, and, therefore, other a 
much less certain modes of determining any forward transfer of po among a 
remain. And, further, as the conclusions we may arrive at hold sentially ei 
classes of animals, only in case other conditions in the structure are the grade i 
the inferences from such evidence can ordinarily extend only to ' 
the family or smaller group to which the species belong. 
