d'Acclimat_.

tome viii.p.

351) stated "that young shells taken from the shores of England and placed in the Mediterranean at once altered their manner of growth, and formed prominent diverging rays _like those on the shells of the proper Mediterranean oyster_;" also to Mr.
Meehan, as stating (_Proc.Acad.Nat.Sc.of Philadelphia_, Jan.

28, 1862) "that twenty-nine kinds of American trees all differ from their nearest European allies in _a similar manner_, leaves less toothed, buds and seeds smaller, fewer branchlets," &c.

These are striking examples indeed! But cases of simultaneous and similar modifications abound on all sides.
Even as regards our own species there is a very generally admitted opinion that a new type has been developed in the United States, and this in about a couple of centuries only, and in a vast multitude of individuals of {89} diverse ancestry.