178 Dana on the Classification of Animals 
nate—which is, that the force may vary in cephalic concentrahon, 
and thereby in its distribution along the principal body-axis. : 
It has been shown in this and the former articles that there is 
been illustrated from all departments of the animal kingdom; 
and with examples from Herbivores in the preceding pages. We 
refer again to the facts among Crustaceans in this Journal (vol. 
xxii, 14, 1856, and the chapter in the author’s Expl. Exped. 
Report, p. 1412,) as especially clear and conclusive, and as hav- 
ing peculiar interest because historically the source in the Wir 
ter's mind of the principles here explained. 3 
Moreover, this backward transfer of force and function manl- 
fests itself also in the posterior elongation of the structure and 
also in some anterior dilation. Conversely, elevation of grade 1s 
manifested in the abbreviation of the structure behind, and to 
extremity is at its maximum under any type, the structure pe 
prosthenic in the highest degree possible for that type. But 
the anterior extremity of the body-axis is not in this maximum 
State, owing to a diffusion of the force posteriorly, the condition 
1s one less prosthenic; by a further loss and diffusion posteriorly; 
there may be another step down (for such transitions, as we bavé 
before found, appear to be by a saltus) perhaps to a lower grade 
methods of dece i ; 
Seek is « li os os apocentric distribution of force—or io 
perfect expression of the fact. “hh 
_* In my last article (Art. IT, p. 1 ificate and retroferent 
ethods of decephali ( es p. 10) I have referred the amplificate anc a away 
or centre. This, although true, is but 
