330 Dana on the Classification of Animals 
of cephalization. 
G. GEOGRAPHICAL DISTRIBUTION. . 
16. Habitational—(1.) Terrestrial species higher than aquatic.— 
This law, announced by Agassiz, is also directly dependent on 
the conditions determining the grade of cephalization. ; 
a. In the case of aguatic species, the ova, as well as the adult 
animals, are bathed in a liquid that penetrates to the interior, 
and dilutes, to some degree, the nutrient or developing fluids ; 
and, under such circumstances, the grade of chemical or vi 
evolution cannot be as high as in the atmosphere. The germ 
must therefore be one of an inferior kind. Aquatic animals are, 
in an important sense, diluted animals. 
often a profounder value than prematurity. The inferior division 
of a cluss, order, tribe, and even subordinate group, is often one 
em 
(aquatic in habit though not strictly so in mode of life, or aquatic — 
in the young state when not in the adult). : ee. 
(2.) Living (a) in impure waters, or those abnormal in condition; — 
or (b) in deficient light, as in shaded places, or the ocean's depths, 
_ mark of inferiority —Muddy waters, or salt waters excessively 
oe oa some inland lakes, or waters only brackish, are here oF 
