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REVIEWS. 
Art. I. Cours de l Histoire Naturelle des Mammiferes. Par M. 
Geoffroy Saint-Hilaire. Paris, 1829. 1 vol. 8vo. 
Tuts work contains the lectures which its celebrated author 
delivered, in 1828, at the Jardin du Roi. They were pub- 
lished separately immediately after their delivery, not with the 
permission merely, but under the superintendence of the Pro- 
fessor, to satisfy, as he tells us, the eager longings of the 
Parisians after useful knowledge; and have none of those 
inaccuracies which disfigure the lectures reported in the heb- 
domadal periodicals of our own country. 
A principal object of the author is to defend and illustrate 
a theory of animal organisation which properly originated 
with him, and of which: he continues to be the most able ad- 
vocate. ‘The theory i is, that all animals are constructed after 
one model, or, in other words, the or ganisation of them may 
be reduced to a uniform type; so ‘hat every part which is 
found in each class has an analogous part in the other classes. 
It is admitted that the parts considered analogous in two ani- 
mals somewhat distant in the scale of being are apparently 
very dissimilar in form, and are appropriated to seemingly 
different functions; but, on attentive examination, intermediate 
forms appear, and the one slides insensibly into the other, 
every change bringing with it a corresponding modification 
of the uses of the part. All the bones, for example, in the 
cranium correspond to one another in all animals which have 
a cranium; not in figure or proportions, for in that they 
obviously differ; nor in use, for a slight alteration of form is 
often accompanied with a change in function; but they are 
analogous in number, and essentially in position and structure. 
Thus, by comparing the foetal head of a quadruped with that 
of a reptile, Saint-Hilaire discovers relations in the number 
and arrangement of the component pieces, which were not 
previously perceived. In the same manner, the os quadratum 
in birds is proved to be analogous to the tympanum of the 
mammalia; and the bony or scaly appendages to the branchiz 
of fish, which are known by the general name of opercula, 
and are concerned in the mechanism of the respiration of 
