External and Internal Factors in Evolution 303 
vessels.” By preventing tadpoles from leaving the water, 
Geoffroy claims that it has been shown that they can be 
prevented from changing into frogs. The main point that 
Geoffroy attempts to establish is no doubt fairly clear, but 
the way in which he supposes the change to be effected is 
not so clear, and his ideas as to the way in which new change 
may be perpetuated in the next generation are, from our more 
modern point of view, extremely hazy. It is perhaps not 
altogether fair to judge his view from the standpoint of the 
origin of adaptive structures, but rather as an attempt to 
explain the causes that have brought about the evolution of 
the organic world. 
During the remainder of the nineteenth century there 
accumulated a large number of facts in relation to the action 
of the external conditions in bringing about changes in 
animals and plants. Much of this evidence is of impor- 
tance in dealing with the question of the origin of organic 
adaptation. 
The first class of facts in this connection is that of geo- 
graphical variation in animals and plants. It will be im- 
possible here to do more than select some of the most 
important cases. De Varigny, in his book on “ Experimental 
Evolution,” has brought together a large number of facts of 
this kind, and from his account the following illustrations 
have been selected. He says: “When the small brown 
honey-bee from High Burgundy is transported into Bresse— 
although not very distant—it soon becomes larger and 
assumes a yellow color; this happens even in the second 
generation.” It is also pointed out that the roots of the 
beet, carrot, and radish are colorless in their wild natural 
state, but when brought under cultivation they become red, 
yellow, etc. Vilmorin has noted that the red, yellow, ane 
violet colors of carrots appear only some time after the wild 
forms have been brought under cultivation. Moquin-Tandon 
has seen “gentians which are blue in valleys become white 
