322 Dana on the Classification of Animals 
It follows, further, from the cephalized nature of an animal, 
that its primary centre mt force, or the point from which concentra- 
tion and the reverse are to be measured, anteriorly and 
riorly, is in the head, near the iio extremity of the struc- 
ture. In an Insect or Crustacean, its position is between the 
mouth and the organs of the senses—over which part the ce- 
phalic mass is located. This is sustained by cnet and 
also by the fact, that, as the two most fundamental c 
1. Methods of Cephalization. 
The methods, according to which the grades of cephalization 
are exhibited, may be arranged under the following heads: 
A (force-measured) of life-system: each type, between Man 
at one extreme and Protozoans at the other, having its special 
range of variation in this respect. 
B. Functional: or variations as to the distribution of the 
functions anteriorly and posteriorly, and as to their condition. 
C. Incremental: or variations as to vegetative increment, that 
is, as to nie me cae and multiplicative development. 
Structural: or variations in the indies of the structure, 
—-whether @ a yaar - on the other hand, resolved into 
normal elements; (2) simple, or complex by specialization ; (3) 
defective, or perfect ; (4), raver sive or plant-like. 
E. Postural: or variations as to posture. (Only in Vertebrates.) 
F. Bintrelogia or variations connected with the develop- 
ment of the you 
G. y erik re | distribution. 
For greater convenience and uniformity, the methods under 
these heads are mentioned beyond as they appear when viewed 
along the descending line of grade, instead of the ascending. 
This is, in fact, the more natural way, since the typical form in 
a group—the fixed point for reference—holds a position towards 
the top of the gro The methods, as given, are therefore 
more strictly ‘akahiods of decephalization than of mips: 
but the former are simply the reverse a the latter. 
A. SIzeE (OR FORCE) OF LIFE 
1. Potential—Exhibited in isa iad less force and size of life- 
system with decline of grade (and the reverse, with rise 
* There m 
one or more secondary centres 
the ect bef f el small The i ° 
regards cbc bt ore us, of compartively *Gastace egphgon $0 
centres of force; but they are, a8 
Bed se splined shewiere by the rte. jargon the Classification of 
Crustaceans referred 
