1 6 INTRODUCTION 



is a branch of zoology which can scarcely be said to be organized, 

 but it is a commonplace to say that animal form and colour have 

 always proved more or less attractive to painters, sculptors, and 

 human beings in general. The uses of animals, parts of animals, 

 or animal products for ornamental purposes fall to be treated of 

 by economic zoology. The old idea was that the beautiful or 

 striking forms and colours of plants and animals were intended 

 solely for the gratification of human tastes. Modern theory inter- 

 prets them as playing some part with reference to the organisms 

 themselves. Predatory animals are often coloured so as to render 

 them inconspicuous to their prey, while, on the other hand, many 

 creatures are thus protected to some extent from their enemies. 

 Conspicuous colours and markings, such as those of the wasp, may 

 be of "warning" nature, acting as danger-signals, while some of 

 the most beautiful tintings are plausibly explained as " courtship 

 colours ", e.g. the brilliant scarlet hues assumed by the male 

 stickleback during the nesting season. 



8. The Philosophic Stand-point. — The groundwork of zoology 

 undoubtedly depends on observation of the various classes of facts 

 enumerated under the preceding headings, but this is not the 

 highest development of the subject. Here the palm must be 

 given to zoology considered as a branch of philosophy, aiming at 

 the explanation of the facts relating to animal form, function, and 

 distribution by means of theories founded on such facts. Thus 

 we see an otherwise chaotic mass of material falling under general 

 laws, and assuming orderly proportions, as in the sister sciences 

 of astronomy, chemistry, physics, and geology. All intelligent 

 workers in the zoological field, whatever may be their special 

 branch — form, function, development, classification, or what not, — 

 adopt the philosophic stand-point more or less, for without a 

 reasonable admixture of theory the subject-matter of zoology is 

 but as bread without leaven, or meat without salt. 



Although speculation, often crude, it is true, has always been 

 more or less associated with the study of living beings, its influence 

 as a revolutionary and stimulating agent undoubtedly dates from 

 1859, the year in which Darwin and Wallace formulated their 

 theory of evolution. And it is the especial glory of zoology 

 that the theory then propounded has had the most wide-reaching 

 influence, not upon biology alone, but upon every branch of 

 learning. For biology connects on the one hand with subjects 



