THE PROBLEM STATED. 9 



'"sexual selection" Mr. Darwin accounts for many of the special 

 features and possessions of animal races. Thus, the song of birds, 

 the brilliant plumage and colours of many species, and the curious 

 .and peculiar ornamentation of many forms, altogether inexplicable 

 on any ordinary theory of utility, are seen to be useful or necessary 

 .adjuncts, on the theory of " sexual selection," to the modification of 

 species and to the evolution of new races. 



The foregoing statement of the Darwinian theory will enable the 

 reader to follow with greater advantage the arguments and illustra- 

 tions adduced in the succeeding chapters in support of the evolution 

 theory at large. It only remains in the present instance to indicate 

 the order and succession in which the evidences of evolution are 

 herein presented. 



An account of the methods in which the study of modern biology 

 'Or natural history is carried out, forms the subject of the second 

 chapter. Such an account will serve to place the reader in posses- 

 sion of the chief data, from a knowledge of which the naturalist is 

 enabled to construct a reasonable and harmonious series of details 

 respecting the living denizens of the globe. The special inquiries of 

 the biologist are duly noted, and the divisions of biology which supply 

 .answers to the pertinent queries of the scientific investigator are 

 .also detailed. Incidentally, the bearings of ordinary biological details 

 on evolution are also discussed, and a suitable introduction is thus 

 .afforded for succeeding studies. 



In the next and third chapter, the reader is made acquainted 

 with the constitution of the animal and plant worlds. The know- 

 ledge of the general relationship of animals and of plants to each 

 other, viewed in groups and as individuals, forms a necessary founda- 

 tion for all biological studies, whether viewed in reference to the 

 theory of evolution, or merely as a part of ordinary information re- 

 specting the universe of life as a whole. In this chapter, the bearings 

 of the constitution of the animal and plant kingdoms on the theory of 

 descent are duly detailed ; and a sketch of the primary classifications 

 of animals and plants is also included in the general history of the 

 worlds of life. 



The fourth chapter introduces the subject of " protoplasm." On 

 the due appreciation of the relations of this substance as the 

 " physical basis of life " to the constitution of the living body, rests 

 the clear understanding of many fundamental points in connection 

 with animal development. Similarly, the inferences which the evolu- 

 tionist is led to draw from the universality of protoplasm as the 

 common material of living beings, are only appreciable when the 

 nature of this curious and all-pervading substance is set forth in 

 detail. No step is possible in biological advance until the facts 

 relating to protoplasm and its relations to life are mastered \ and in 



