based on the principle of Cephalization. + 26t 
of Odtocoids under Mammals, which has its megasthenic and mi- 
ee subdivisions ; under Worms, wi 
4, Distinction between Animals and Pla 
XI. This subject well illustrates a Pee SBS distinction 
between animals and plants. 
a. An animal, as has been stated on page 332, has fore-and-aft, 
or antero-pos sterior, polarity; that is, it has a fore-extremity and 
a hind-extremity whi ch have that degree of oppasitepess that 
ee ss rity. 
b. this fore- and-aft polarity there is also dorso-ventral 
cn see a 
c. The dorso-ventral and antero-posterior axes are at right 
angles to one another. In Invertebrates and a large part of 
Vertebrates the an tero-posterior axis is horizontal and the dorso- 
ventral vertical; and only in Man, the prince of Mammals, is 
the woe vertical and the latter horizontal. 
nimal, again, has not only oppositeness between the 
dere extramity and hind- -extremity, but also a head, the seat of 
the senses and mouth, situated at the Serecxiceinity Ka con- 
Stituting this extremit 
e. In Sabon, be typical animal i is forward movin 
mary centre in an animal (p. 822)—is not placed at one extremity, 
but is more or less nearly central; and almost precisely central in 
the symmetrical (and therefore inferior) Radiates. The mouth- 
extremity and the opposite are at the poles of the dorso-ventral 
axis, and not at those of the antero-posterior; that is, they 
are at the extremity of the axis which in the inferior animals is 
normally vertical. This is true even in a Holothuria, the mouth 
of which is not at the anterior Sarre, but is central, or nearly 
80, asin an Kchinus. A Limulus en referred to on n page 
828 as showing an approximation, unde the true animal type, 
to this same central position of the mo 
We pass now to Plants. The slant, j in contrast with the fore- 
and-aft animal, is an wp-and-down structure, having up-and-down 
polarity. The axis is vertical like the dorso- -ventral 1 in the lower 
animals, to which it is strictly anaes as is shown from a 
comparison with Radiates,—Radia and Plants bee alike in 
type of structure. The primary ae of force is central, in the 
Same sense, in the regular flower and the symmetrical Radiate, 
Thus, the structures under the animal-type and plant-type are 
on two distinct axial directions, one at right angles to the 
other: in the animal-type the antero-posterior axis being the 
dominant one, while the two coexist; and in the plant-type the 
axis at right angles to this being the only one. 
