THE PROBLEM STATED. II 



be said to regard the deductions of embryology amongst the chief 

 supports of their hypothesis. Hence, as the subject is not merely 

 important in itself, but also somewhat technical in details, it has been 

 judged advisable to discuss the problems of development at some 

 length. In chapter ninth, the earlier stages in the development of 

 animals at large form the chief topics treated. In the tenth section, 

 two special groups the Echinoderms or star-fishes, &c., and the 

 Crustaceans (or crabs, lobsters, and their allies) are selected for 

 discussion ; whilst in the succeeding section attention is directed to 

 the special features observable in the development of the Molluscs, 

 and of higher animals still. 



The twelfth chapter, devoted to the " metamorphosis " of insects, 

 is intended specially to show how the development of these animals 

 presents us with a series of highly interesting illustrations of certain 

 modifications affecting the young of animals as well as the adults. 

 The origin of the wings of insects, and other details incidental to the 

 structure and physiology of these animals, are also discussed in this 

 chapter. 



The thirteenth chapter revises, somewhat at length, certain 

 problems in the constitution of animals which appear worthy of 

 study ; whilst incidentally the nature of the plant-constitution is 

 also treated. Both topics are related to evolution in a broad sense ; 

 since the factors which determine the intimate constitution of the 

 animal or plant must also perforce possess a large share of influence 

 in modifying the worlds of life at large. 



The fourteenth chapter, dealing with,the "fertilisation of flowers," 

 is intended to illustrate certain of the methods whereby, in the 

 physiology and life of plants, the evolution of new races is favoured 

 and assisted. No more typical examples of ways and means adapted 

 to aid and inaugurate the primary conditions on which evolution 

 depends and to ensure variation, could well be cited than this 

 department of botanical science. The deductions from flower- 

 fertilisation tend very powerfully, moreover, to support the doctrine 

 of descent in other phases than those which are connected merely 

 with plant-reproduction at large. 



The fifteenth chapter, devoted to the subject of " degeneration," 

 exemplifies the axiom that the ways of evolution include backsliding 

 and retrogression as well as advance. Many animals and plants have 

 developed all their characteristic features through their adoption of, 

 and adaptation to, a lower way of life than that pursued by their 

 ancestors ; whilst whole groups of animals present features to the 

 naturalist which could not be accounted for by any ordinary phase of 

 evolution, but which the idea of degeneration, as a factor in working 

 out the ways of life, has fully explained. 



The concluding chapter deals with the relations of geological 



