Introductory Sketch. 17 



All these and many other points have been deeply investigated, 

 and are now the common property of naturalists. 



But up to the present no one has attempted systematically to 

 find out the principles or laws which govern the distribution of 

 colouration ; laws which underlie natural selection, and by which 

 alone it can work. Natural selection can show, for instance, how 

 the lion has become almost uniform in colour, while the leopard is 

 spotted, and the tiger striped. The lion living on the plains in open 

 country is thus rendered less conspicuous to his prey, the leopard 

 delighting in forest glades is hardly distinguishable among the 

 changing lights and shadows that flicker through the leaves, and 

 the tiger lurking amid the jungle simulates the banded shades of 

 the cane-brake in his striped mantle. 



Beyond this, science has not yet gone ; and it is our 

 object to carry the study of natural colouration still further : to 

 show that the lion's simple coat, the leopard's spots, and the tiger's 

 stripes, are but modifications of a deeper principle. 



Let us, as an easy and familiar example, study carefully the 

 colouration of a common tabby cat. First, we notice, it is darker 

 on the back than beneath, and this is an almost universal law. It 

 would, indeed, be quite universal among mammals but for some 

 curious exceptions among monkeys and a few other creatures of 

 arboreal habits, which delight in hanging from the branches in such 

 a way as to expose their ventral surface to the light. These 

 apparent exceptions thus lead us to the first general law, namely, 

 that colouration is invariably most intense upon that surface upon 

 which the light falls. 



As in most cases the back of the animal is the most exposed, 

 that is the seat of intensest colour. But whenever any modification 

 of position exists, as for instance in the side-swimming fishes like 

 the sole, the upper side is dark and the lower light. 



The next point to notice in the cat is that from the neck, along 

 the back to the tail, is a dark stripe. This stripe is generally con- 

 tinued, but slighter in character across the top of the skull ; but it 

 will be seen clearly that at the neck the pattern changes, and the 

 skull-pattern is quite distinct from that on the body. 



From the central, or what we may call the back-bone stripe, 

 bands pass at a strong but varying angle, which we may call rib- 

 stripes. 



Now examine the body carefully, and the pattern will be seen 



