32 CHAPTERS ON EVOLUTION. 



construction of artificial systems of classification represented the 

 chief labours of the biologists of past years. But impelled by the 

 researches of Cuvier, who laid the foundations of morphology, and 

 who clearly mapped out the animal world into four great types 

 three of which to this day remain much as his genius left them 

 biology awoke to a new lease of life. Placed in possession of some 

 definite aim in the investigation of animal structure, zoologists began 

 the systematic examination of the great divisions of the animal world 

 which Cuvier had mapped out. Next in order came the era marked 

 by the speculations of Lamarck, in turn succeeded that characterised 

 by the imperishable deductions and suggestions of Darwin. Then 

 was supplied the guiding clue, for want of which zoology and botany 

 had been left to progress in slow and desultory fashion. The impetus 

 given by Darwinism and evolution to biology may be fully appreciated 

 when we reflect that in evolution we perceive the suggestion of a 

 rational purpose in the researches we undertake into the structure, 

 physiology, and distribution of living beings. When we discover that 

 life everywhere exhibits progress, that the development of animals 

 and plants has been a work of progress in the past, that modification 

 proceeds apace even now, and that it is possible to discover the 

 clear plan and method of creation in the forms and development of 

 living things, we may readily appreciate the incentives to research in 

 all directions which the idea of evolution, as the method of nature, 

 has given to the biology of to-day. 



Understanding something of the theory of the living universe, the 

 biologist can set himself to work hopefully to unravel many of the 

 so-called mysteries of life. Asking himself regarding every living 

 thing the question, " How has it come to occupy this or that place 

 in nature ? " he firstly studies its development as a clue to its descent 

 and origin. The modern biologist looks to development, above all 

 else, to teach him the true nature and relationships of animals and 

 plants. If a sea-squirt's development runs in parallel lines to that 

 of the lowest fish, then he naturally concludes that like results in 

 this case follow from similarity of origin, and fishes and sea- 

 squirts become organically connected through community of descent. 

 If a Sacculina (existing as a mere parasitic bag of eggs on a hermit 

 crab) passes through essentially the same stages in its development 

 as a shrimp, a water-flea, a barnacle, a crab, and all other crus- 

 taceans, he feels bound to believe that these varied forms have 

 sprung from one and the same root-stock. If he finds that a 

 frog in its early life is essentially a fish in structure and physiology, 

 he assumes that he is being taught the descent of the frog-race 

 from aquatic and fish-like ancestors ; otherwise, why, he may reason- 

 ably ask, should nature trouble herself to develop a fish-stage in 

 the formation and growth of the land-inhabiting frog ? If he finds 



