. 
that far profounder knowledge is requisite for unfailing aoa 
158 Dana on the Classification of Animals 
development or growth, and ()) through all the steps in the ~ 
progress of growth, as well as (c) in the resulting structures, 
The above general facts are at the foundation of all the — 
methods of cephalization, or decephalization, pointed out in Ar ~ 
ticle I. They receive further illustration in the pages beyond, 
ot pase explanations on pages 175 to 182. i 
eee ee 
he con: 
tremes of cephalization is one source of the difficulties in the 
subject of classification. But the law cannot, on account of the 
trouble it may give, be condemned; for, as I have before 1 
marked, it is in accordance with universal truth that smallness, 
or circumferential contraction, should proceed both from concel 
tration, and from lack of quantity, although these are opposil® 
conditions. The difficulties in the way of a right use the 
principle of cephalization are, therefore, in nature, and must 
met by the only legitimate means—thorough study. be 
But he believes that the principle appealed to is right an fon. 
damental; and if he ventures to present new classifications © 
departments in zoology in which adepts in these departmen 
have made trials with diffierent results, it is only to offer such 
animal kingdom were considered. In the second, one 
Orders was reviewed and an arrangement given of its suv! 
sions, down to the grade of Tribes. In the present, the 
cation of a Z'ribe is followed out, down to the grade of Fan 
