170 J. D. Dana on Cephalization, 4 
A 
the criterion referred to is made superior to all others, or the 
most decisive of grade, and not perceiving, therefore, that the 
reductio ad absurdum, intended for the principle criticised, at- 
i gain, by a similar misuse of the 
criterion connected with prehensile anterior limbs, and additional 
misunderstandings already alluded to, he arrives at other absurd- 
ities. In the same way he might assume that, because great 
length of antennz is one of the marks of low grade,—the Mac- 
rurans (Lobsters, Shrimps, &c.,) showing by this character, as I 
have stated, their inferiority to Brachyurans (Crabs),—therefore 
Insects ought to be arranged according to length of antenn®; 
which would of course make very heterogeneous assemblages. 
Or he might next make abdomens or tails the grand criterion, 
(this characteristic being also set down as a mark of grade), with 
a like result. By thus assuming successively that each criterion 
is superior in value to the others, all may run into the 
ground; a feat of no great prowess in logic or science. 
While long antennz and long abdomens are among the marks 
of that decentralization or decephalization which distinguishes 
the Macrurans from the Crabs, some of the higher Macrurans 
have, relatively to size of body, longer antennz than the lower; 
and there are hundreds of Tetradecapods and Entomostracans, 
still inferior species, that have relatively to length of body, far 
shorter antennz, and shorter abdomens too, than the Macrurans. 
There are, in all such cases, characters to be considered of higher 
value before we come down to that level where length of an- 
tenn, or of abdomen, is decisive as a mark of grade. 
7. As Nature is yet an unfathomed deep, our systems must 
have their imperfections and uncertainties, and we our difficul- 
ties in applying principles that have been ascertained. Hxam- 
ples of such difficulties from the subject of cephalization have 
een alluded to in the preceding remarks; and here is ae 9 
a mark of, inferior grade. Man is smaller than his inferior the 
Lion; the Lion is smaller than its inferior the Hippos 
the Hippopotamus than its inferior the Whale; the Crab than 
its inferior the Lobster; the Echinus than its inferior a larg® 
