114 FOOT-NOTES TO EVOLUTION. 
which will serve as an illustration of a whole class: 
Jackson * says that the elongated siphon of Mya, the 
long-necked clam, is due to its habit of burrowing in 
the mud, or to quote his words: “It seems very evi- 
dent that the long siphon of this genus was brought 
about by the effort to reach the surface, induced by the 
habit of deep burial.” It certainly would be pertinent to 
inquire where it got this habit, and how it happened to 
be transmitted. It is surely as difficult to explain the 
acquisition and inheritance of habits, the basis of which , 
we do not know, as it is to explain the acquisition and 
inheritance of structures which are tangible and visible. 
Such a method of procedure, in addition to begging the 
whole question, commits the further sin of reasoning 
from the relatively unknown to the relatively known. 
This case is but a fair sample of a whole class, 
among which may be mentioned the following: The 
derivation of the long hind legs of jumping animals, the 
long fore legs of climbing animals, and the elongation of 
. all the legs of running animals through the influence of 
an inherited habit. All such cases are open to the very 
serious objection mentioned above. 
(y) Another whole class of arguments may be re- 
duced to this proposition: Because necessary mechan- 
ical conditions are never violated by. 
organisms, therefore modifications due 
to such conditions show the inheritance 
of acquired characters. Plainly, the alternative propo- 
sition is this: If acquired characters are not inherited, 
organisms ought to do impossible things. 
(2) Many of the arguments advanced to prove the 
inheritance of characters acquired through use or dis- 
use seem to me to prove entirely too much. For ex- 
Mechanical 
conditions. 
*R. T. Jackson. Memoirs Boston Soc, Nat. Hist., 1890. 
