and the Elements in which they live. 385 
tribes in tertiary beds; and there will be no doubt left that the 
gradation of structure is intimately connected with the extension 
of continental lands, and that the present connection of animals 
with the surrounding media in which they live agrees also with 
their natural gradation. If we would study the natural relations 
between animals.and the media in which they live, we could not 
begin with better prospect of success than by investigating mi- 
“ 
“nutely the different families of Vertebrata separately, rather than 
“the whole classes of this great type. For though it is at once 
apparent that the class of Fishes as a whole is entirely aquatic, and 
stands at the same time lowest among Vertebrata, as soon as we 
pass to the investigation of the Reptiles we find aquatic and even 
marine types among ‘Turtles, which rank much higher than the 
whole order of Batrachians, which are almost entirely fluviatile ; 
and we find again marine and fluviatile types among Birds an 
Mammalia, the highest of all Vertebrata. These facts show most 
, conclusively that an organization aS-high as that of the Vertebrata 
Ba thee] 2 peered a, Neen, ie as sd 
rd 
_ Introducing a mode of exi 
f ae ee 
the seasons throughout the. year, so durable as to last for numbers 
of years, (whilst among Invertebrata, and especially among Insects, 
but also among many other animals of lower type, there exists 
the most:intimate connection between their development and the . 
course of the seasons); we say these facts show that with such ani- 
mals which are placed so far above the influerice of physical con- 
ditions, their connection with the circumstances under which they 
live is much weaker, so much so that internak stracture overrules 
greatly the foundation of thoge conneetions Which are so intimate 
in lower animals, and reduces their limits ‘to subordinate connec- 
tions between members of the minor groups; while in the ¢ 
of Fishes—the lowest—the whole type is orgahized in such a 
manner as to make it uniformly dependent upon one»of the 
natural elements in which animals live,*¢he three other classes 
present most. diversified combinations, *there being marine, flu- 
Viatile, and: terrestrial or aérial types in these classes, under the 
development of as many structural types, differing almost in the 
ree when contrasted with each other and so much 
that the aquatic Mammatia even in their marine types, or the ma- 
tine Turtles, differ as much from each other or from Birds as they 
agree with their respective fresh water or terrestrial types. ‘These 
discrepancies between the great types may be owing to other 
motives in the plan of creation than those to which they are 
here ascribed. ‘The apparent anomalies between some of the 
articulated types may also be the results of combinations different 
from those with which they aré¢onnected above. But whether 
views are correct or not, have no doubt that the study of 
the phenomena which I am now contrasting, cannot fail to lead 
y to a more correct appreciation of the natural relations 
Szcoxp Series, Vol. IX, ‘No. 27.—May, 1850. 9 
