Geological Soceety of London. 113 
the evidence afforded by a few bones or other relics preserved in a 
fossil state. He has described the parts of the living animal or plant 
most nearly analogous to those which are found buried in the earth, 
usually illustrating by figures the distinctness and at the same time 
the resemblance of the recent and extinct species, showing that all 
are parts of one great scheme, and that the lost species even supply 
links which are wanting in the existing chain of animal and vegetable _ 
creation. 
It is impossible to read the account given of the Megatherium, 
and to contrast it with that drawn up by Cuvjer of the same species, 
without being struck with the increased interest and instruction, and 
the vast accession of power derived from viewing the whole mechan- 
ism of the skeleton in constant relation to the final causes for which 
the different organs were contrived. 
The chapter on saurian and other reptiles. has afforded the Pro- 
fessor another beautiful field for exemplifying the infinite variety of 
mechanical contrivances and combinations of form and structure 
which the fossil representatives of that class exhibit. 
The account also of the Cephalopodous Mollusca, so many thou- 
sands of which are scattered through the strata, and which until very 
recently have presented so obscure a problem to the naturalist, is full 
of original observation. ‘The history of the animals which formed 
the Belemnites, of which it appears that nearly one hundred species 
are now known, and the proofs adduced that they were provided 
with ink-bags like the cuttle-fish, the description also of the fossil 
pen-and-ink fish, or Loligo, and other sections of this part of the 
Treatise, carry our information respecting the family of naked Ce- 
phalopods much farther than was ever attempted in any previous 
work. Nor should I omit to mention the exposition of an ingenious 
theory for the use of the siphuncle and air-chambers of the Ammo- 
nite, which, whether confirmed by future examination or not, be- 
comes in the author’s hands the means of conveying to the reader a 
clear and well-defined notion of the varied forms and complicated 
structure of these shells, and of awakening a lively desire to under- 
stand thei singular organization. | 
I may also recall to your notice the just and striking manner in 
which certain physical inferences are drawn from the conformation of 
the eyes of extinct Crustacea, such as the Trilobite. .The most deli- 
cate parts of these organs are sometimes found petrified in rocks of 
high antiquity, and it is justly observed, that such optical instru- 
Vou. XXXIL.—No. 1. 15 
