e lamprey and fishes to the
mammals is not a regularly gradated one, and accounts for this "because
the work of nature has been often changed, hindered, and diverted in
direction by the influences which singularly different, even contrasted,
circumstances have exercised on the animals which are there found
exposed in the course of a long series of their renewed generations."

Lamarck thus accounts for the production of the radial symmetry of the
medusae and echinoderms, his _Radiaires_. At the present day this
symmetry is attributed perhaps more correctly to their more or less
fixed mode of life.

"It is without doubt by the result of this means which nature
employs, at first with a feeble energy with _polyps_, and then with
greater developments in the _Radiata_, that the radial form has been
acquired; because the subtile ambient fluids, penetrating by the
alimentary canal, and being expansive, have been able, by an
incessantly renewed repulsion from the centre towards every point of
the circumference, to give rise to this radiated arrangement of
parts.

"It is by this cause that, in the Radiata, the intestinal canal,
although still very imperfect, since more often it has only a single
opening, is yet complicated with numerous radiating vasculiform,
often ramified, appendages.

"It is, doubtless, also by this cause that in the soft Radiates, as
the medusae, etc., we observe a constant isochronic movement,
movement very probably resulting from the successive intermissions
between the masses of subtile fluids which penetrate into the
interior of these animals and those of the same fluids which escape
from it, often being spread throughout all their parts.

"We cannot say that the isochronic movements of the soft Radiates
are the result of their respiration; for below the vertebrate
animals nature does not offer, in that of any animal, these
alternate and measured movements of inspiration and expiration.
Whatever may be the respiration of Radiates, it is extremely slow,
and is executed without perceptible movements" (p. 200).

_The Influence of Circumstances on the Actions and Habits of Animals._

It is in Chapter VII. that the views of Lamarck are more fully presented
than elsewhere, and we therefore translate all of it as literally as
possible, so as to preserve the exact sense of the author.

"We do not here have to do with a line of argument, but with the