based on the principle of Cephalization. 331 
But oceante waters, although saline, are not properly impure. 
Of the subkingdoms and the classes containing aquatic ani pe 
_ the highest groups are those of marine waters. Thus, the highest 
of Mollusks, the Cephalopods, are marine; the highest of Radi- 
ates, the Echinoderms; the highest of Fishes, the Selachians; of 
Crustaceans, or the Maioid or Triangular Crabs; of Worms, 
the Dorsibranchs; of Acalephs, all but the Hydroids are ma- 
rine; while all species of Echinoderms and Polyps are marine. 
Among the subordinate groups there are some fitted particu- 
larly for fresh water. Types that belong to fresh water some- 
times have inferior species in brackish or salt water; and those 
that belong to salt water sometimes have inferior species in 
brackish or fresh water. 
(3.) Species of cold climates inferior to those of warm.—Accord- 
ing to the J5th canon, the highest oviparous animals should be 
tropical species; but not necessarily so the viviparous Mammals 
since, with them, the requisite temperature for embryonic devel- 
opment is obtained within the parent 
Tange of the world—the one because so low, the other, so high. 
g accompanies Man in his wide wanderings: but te 
. Recapitulation.—The following are the names of the several 
_ Methods of cephalization pointed out, both those based on the 
descending and ascending lines of grade. 
Am. Jour. Sct.—Srconp Serres, Vou. XXXVI, No. 108.—Nov., 1863, 
43 
