J. D. Dana on Zoiphytes. 339 
connected with the causes just mentioned. Under the several 
grand divisions to which we are led by the above considerations, 
there are subordinate variations arising from the i 08 of life 
to minor differences in the conditions of existence around us :— 
food of whatever iin d, and in some peculiarities of the omuiies 
digestion ; certain. differences depending on the sexual relations, 
and the means of preserving and developing the young, varying 
with the modes of existence alluded to; modifications of the provis- 
caer ee neem against enemies. 'These minor differences 
exhibited in two ways: either particular organs retaining the 
am functions, undergo modifications in form and structure ; or 
with other modifications, they subserve the to rs diffe ent 
functions. When adaptations to different circumstances or pur- 
and the relations are analogical, when they depend on a simi- 
larity of function, a produced.* 
As the several families or classes of animals are exposed, in 
some respects more or less to the same 
they would naturally undergo, in many instances, either homo- 
or analogical modifications, occasioning that serial paral- 
lelism alluded to oh a preceding page. And again, as the ammals_ 
of the same os may be fitted to many aes circumstances 
in nature, other paralielisms should exist, of a w 
The order i in which the above sources of dhaiettions in the 
animal kingdom are —" may be in the main nearly that 
re «Ree PRC ton ET 
pital bone in Man, with the distinct bone called ¢ geet aye in a crocodile or 
bag phoma: ite its special homology is determined.’ —Phil, Mag., xxviii, iii ser., 
une, 846. 
We refer 1S te reader also to a Ay excellent Ae G'S, Ph “on — | Relations 
Jrganized Beings,” by H. E. Strickland, ee 
354, in which the subject ‘ad affinities in organic boas is sea oP a clear 
3 A 
he word alan Seni the re ceabtanen of the flower of 
the p pea toa pee oh or the shell Haliotis to an ear 5 oo it includes also resem- 
blane oe cidence of color; while 
em a. rgcaeher ie Mie 9 upon a ® similarity of function. 
