SECTION XV 

 THE PHILOSOPHY OF ZOOLOGY 



IN dealing with the structure and development of the various 

 groups of animals, there has been occasion not infrequently to refer 

 incidentally to various subjects of a general nature, such as 

 evolution, heredity, and the like. Such topics, dealing, not with 

 the concrete facts of the science, but with abstract generalisations 

 deduced from the facts, may be grouped together under the 

 general heading of the Philosophy of Zoology. The generalisations 

 forming the subject-matter of the philosophy of zoology may, in 

 some instances, be so clearly and directly deducible from the data 

 concerned, that it is scarcely possible for anyone conversant 

 with the facts to refuse credence to the generalisation. But in 

 other cases the conclusion is a matter of probability only, and one 

 conclusion or another may be regarded as the more probable, 

 according to the estimate formed of the relative importance to be 

 attached to different sets of the facts or to different aspects of the 

 facts. This will become clearer as we proceed ; but at the outset 

 it should be distinctly understood that what follows is not to be 

 looked upon in the same light as the statements regarding the 

 known phenomena of animal life which constitute the main sub- 

 stance of the preceding sections. Nearly all the subjects now to 

 be touched upon are, to a greater or less extent, matters in which 

 there may be variety of opinion among those conversant with the 

 phenomena; they are all subjects which will bear discussion from 

 various sides ; but, as discussion is here almost out of the question, 

 it is possible to give little more than a brief statement of some of 

 the current views on these questions as an introduction to the 

 study of works specially dealing with them. 1 



The Philosophy of Zoology, or the Philosophy of Biology (for it 

 is here almost impossible to treat Zoology apart from its com- 

 panion science of Botany), aims at an explanation of the facts of 



1 See Appendix II, Nos. 2, 3, 4, 13, 14, 15, 16, 18, 32, 38, 46, 47, 48, 

 53, 55, 56, 60, 62, 63, 65, 66, 68, 



