228 PHILOSOPHY OF ZOOLOGY. 
number of concentric circles of the vertebree and scales of 
fishes, have been regarded, in the absence of experience, as 
indicating the age of the animal to which they belong. 
Even the age of the Earth, apparently, in the opinion of 
some geologists, may be determined by regarding its strata, 
as analogous to the layers of growth in a tree. 
An anatomist of eminence observed, that the cells of a 
piece of bee-comb which he examined were double *. The 
acute author of the article, “ Vegetable Anatomy,” in the 
Supplement to the Encyclopedia Britannica yields to the 
opinion, that the cells of plants are double, influenced by 
this observation of the condition of the cells of bees, 
Since the windpipe of birds is employed to convey air to 
and from the lungs,—vegetable physiologists have ever 
been inclined to consider the spiral vessels of plants, which 
have a remote resemblance thereto, as likewise air-vessels, — 
and much vain reasoning and idle conjecture, have in con- 
sequence been displayed on the subject. 
As the materials of the crust of the earth are lighter than 
the mean density of the earth, many geologists conclude, 
that the weighty materials of the centre must be metallic, 
without attending to the condition which must be produced 
by the force of gravitation, or the analogous arrangement 
of the atmosphere. Who ever risked the conjecture, that 
the lower and denser parts of the atmosphere, were of a 
more metallic nature than the higher and lighter parts ? 
On what foundation does the belief rest, that the other 
planets are inhabited, but on that of analogy ; yet the cir- 
cumstances of the other planets are all different with re- 
gard to the force of gravity, motion, temperature, and 
light. Their inhabitants, therefore, if such exist, must be 
unlike us in physical constitution at least,—neither bone of 
our bone, nor flesh of our flesh. 

* Mem. Wern. Soc. ii. p, 259 
