12 THE POPULAR SCIENCE MONTHLY. 



sects connected with a change of food. First, he established the fact 

 that insects accustomed to one kind of plant could acquire a taste for 

 another kind, and he has shown that in thus changing the food of the 

 insect a change took place in the appearance of either the larva, 

 pupa, or imago, and sometimes all three stages were affected. Dr. 

 Fitch had observed that changing an insect's larva from the leaf to 

 the fruit affected the appearance of the larva. It would be impossible 

 to give even an abstract of Dr. Walsh's remarkable essay. It may 

 be said, however, that his investigations led him irresistibly to the 

 conclusion that the present species have been derived from preex- 

 isting ones, and in numberless cases he is capable of showing the 

 successive stages from the dawn of a plant-eating variety, where 

 the changes are slightly seen in the larva only, to the plant-eating 

 species in which profound changes are seen in the larva, pupa, and 

 imago. 



The minor factors of natural selection, such as protective coloring 

 and mimicry, have been variously illustrated by Mr. R. E. C. Stearns, 

 Dr. Kneeland, Prof. Cope, Dr. Charles C. Abbott, and others. In a 

 special paper on " The Adaptive Coloration of Mollusca," ' I have en- 

 deavored to show not only a wide-spread application of this feature 

 to mollusks, and especially those exposed by the tide, but in some 

 cases a mimicry of inanimate objects, as the accumulation of clay or 

 grains of sand upon the shell. 



Wallace's theory of birds'-nests finds interesting confirmations in 

 the observations of Dr. Abbott, who made a special study of a large 

 number of robins'-nests, and found the widest variation among them. 

 He studied also the nests of the Baltimore oriole, where, according to 

 the theory of Wallace, a concealing nest should be made, the bird 

 being exceedingly bright-colored. He found that, away from the 

 habitations of man, the orioles built concealing nests ; but in villages 

 and cities, on the other hand, where they were in no special danger 

 from predatory hawks, the nests were built comparatively open, so 

 that the bird within was not concealed. 8 



The differences in the habits of animals of the same species are 

 noticed in different parts of the country, and such facts militate 

 against the idea that certain unerring ways were implanted in them 

 at the outset. Indeed, such facts go to show that these various creat- 

 ures not only become adapted to their surroundings, but that individ- 

 ual peculiarities manifest themselves. The observations of Dr. Cones, 

 Mr. Allen, and Mr. Martin Trippe, go to prove that certain birds 

 change their habits in a marked degree. In their behavior, too, cer- 

 tain birds, which are wild and suspicious in New England, are com- 

 paratively tame in the West. In their resting-places they show wide 

 individual variation. 



1 " Proceedings of the Boston Society* of Natural History," vol. xiv., p. 141, 

 5 Popular Science Monthly, vol. vi., p. 481. 



