there are to be not more than four, that it is
impossible for it now to see this matter in any other light.

The experiments of M. Brown Sequard on guinea pigs, quoted by Mr.
Darwin,[298] suggest that the form of the serpent may be due to its
having lost its legs by successive accidents in squeezing through narrow
places, and that the wounds having been followed by disease, the
creature may have bitten the limbs off, in which case the loss might
have been very readily transmitted to offspring; the animal would
accordingly take to a sinuous mode of progression that would doubtless
in time elongate the body still further. M. Brown Sequard "carefully
recorded" thirteen cases, and saw even a greater number, in which the
loss of toes by guinea pigs which had gnawed their own toes off, was
immediately transmitted to offspring. Accidents followed by disease seem
to have been somewhat overlooked as a possible means of modification.
The missing forefinger to the hand of the potto[299] would appear at
first sight to have been lost by some such mishap. Returning to Lamarck,
we find him saying:--

"Even in the lifetime of a single individual we can see organic changes
in consequence of changed habits. Thus M. Tenon has constantly found the
intestinal canal of drunkards to be greatly shorter than that of people
who do not drink. This is due to the fact that habitual drunkards eat
but little solid food, so that the stomach and intestines are more
rarely distended. The same applies to people who lead studious and
sedentary lives. The stomachs of such persons and of drunkards have
little power, and a small quantity will fill them, while those of men
who take plenty of exercise remain in full vigour and are even
increased."[300]

It becomes now necessary to establish the converse proposition, namely
that:--

"_The frequent use of an organ increases its power; it even develops the
organ itself, and makes it acquire dimensions and powers which it is not
found to have in animals which make no use of such an organ._

"In support of this we see that the bird whose needs lead it to the
water, in which to find its prey, extends the toes of its feet when it
wants to strike the water, and move itself upon the surface. The skin at
the base of the toes of such a bird contracts the habit of extending
itself from continual practice. To this cause, in the course of time,
must be attributed the wide membrane which unites the toes of ducks,
gees