Page images
PDF
EPUB

lection " seems also to have taken part in the encouragement and perpetuation of variations. The combats of male animals are familiar to every one.

It is the rule, rather than the exception, for the male to fight with other males for the possession of the female; and this is true of animals as wide apart in size and rank as the buffalo (bison) of our Western prairies, and the stag-beetle or “ pinch-bug.” Even if one of the combatants is not killed outright in these duels, the weaker animal, in being defeated, loses the choice of feeding.ground, and, in some cases, the necessary protection of the herd to which he properly belongs; and of course he loses, for the time being at any rate, the opportunity of breeding with any female of the species. It is not even necessary that there should be a combat, or that a contest of strength even, should arise between two of the males, in order to give an opportunity for preference to be shown by the female. Throughout the animal kingdom, almost without exception, it is the male who courts and pursues the female; so that he is in every instance compelled to use all means to secure her favor. And so far as the most competent observers are able to judge of the matter from the behavior of animals, and particularly of male song-birds, at the breeding season, it is allowable to infer that the females of the lower animals are by no means indifferent to what might almost be called the personal attractions of individuals of the opposite sex.

But, if this be granted, it is clear that we must admit that the color or the form, that the power or quality of the voice, as well as courage and physical strength, may be important in influencing the choice by female animals of the sires of the next generation. Here, again, as with natural selection, there would be a strong tendency to retain certain qualities, and encourage their highest development; for any desirable modification would give its possessor so much of an advantage (in the manner just described), that this modification would be very likely to be perpetuated.

So far, in the treatinent of the subject of development, the two theories of the origin of species have been stated; then the amount of variation in all living things has been outlined, its causes have been discussed, as well as the causes which tend to perpetuate new species once formed.

In the coming chapter will be presented some curious and interesting indirect proofs that in both the animal and the vegetable kingdom there has been development of some sort.

CHAPTER V.

- INSECT

MIMICRY AND ALLIED PHENOMENA.

FERTILIZATION.

IT
T has probably been known, ever since men

first began to observe the appearance and the habits of animals, that the latter often take their color and markings, sometimes even their shape, from the objects among which they live. The white winter-dress of the arctic hare and the ptarmigan are only striking instances of a world-wide series of such imitations among animals. Any one who has at low tide ever floated along in a boat over the green and brown gardens of dulse and other seaweeds among which the common flounder lives, and on which he feeds, must have noticed how difficult it is to distinguish his smooth, flat, indistinctly marked upper side (not his back) from the sea-bottom which he hugs so closely.)

i This paragraph was written long before the authors had seen Grant Allen's charming account of the matter.

In many rivers of the Mississippi basin, too, there is a curious fish, the “ hog-sucker,” whose back is so mottled with shades of brown, that even the expectant fisherman, who knows how palatable this sucker is, will often fail to drop in his triple-pointed "jig-hook;" for the fish lying quietly on the creek-bed is very nearly indistinguishable from the stones about him. How hard it is, too, to see the quail (bob-white) or the prairie-hen as it squats under the very muzzle of the gun.

The green dress of the katydid, the gray of moths which alight on the bark of trees, the green color of plant-lice, the transparency of jelly-fish and many defenceless marine animals, the colors of the chrysalist of certain caterpillars found at the Cape of Good Hope, varying with the material to which the chrysalis. is attached — all these further illustrate the kind of imitation just mentioned. Other animals, however, afford still more striking because completer resemblances. Our common stick-bug, or devil's walking-stick, is far outdone by tropical insects of similar form; while the leaf-like katydid is much less perfect in its imitation than a species of phyllium, a kind of leaf-like

1 The nearly or quite immovable condition which caterpillars assume before changing to butterflies.

insect found in Java, of which the distinguished English naturalist, Alfred Russell Wallace, relates that residents on the island often keep one of these insects on a branch of the guava-tree as a puzzle for strangers, who are told that the

[graphic][merged small]

insect is on the tree, but are unable to find it among the leaves. More striking still, if possible, is the resemblance of the leaf-butterflies, as they sit with folded wings, to a leaf of the tree or shrub on which they are in the habit of alighting; so that, even in the figure here

« PreviousContinue »