ANIMALS AND THEIR ENVIRONMENTS. 301 



Later years brought to biology the enriching knowledge of 

 Darwin ; and generalisations regarding the origin of living 

 beings, startling and revolutionising in their nature, were 

 submitted to the scrutiny of the scientific world. But after 

 the first feelings of surprise had passed away, and as the 

 clearness of Darwin's views and their exceeding harmony 

 with the facts of life were observed, biologists gladly hailed 

 his generalisations as affording the basis of a reasonable 

 conception of nature at large. Facts in animal life, hitherto 

 regarded as simply inexplicable, and which were accepted 

 as primary mysteries of biological faith, received at the 

 hands of Darwin new and rational explanations ; and to the 

 eminently plain and consistent nature of the ideas involved 

 in his system of thought, may be ascribed the great success 

 and ready acceptation which evolution has met in the world 

 of thought at large. Amongst other features which this 

 method of thought exhibits in characteristic fashion, is that 

 of assigning a paramount place to the influence of habit and 

 use, and of outward circumstances upon the form and " way 

 of life " of living beings. A few illustrations of the changes 

 which both common and unwonted circumstances of exist- 

 ence may effect in the history of animals, together with a 

 brief chronicle of the influence of such changes on the 

 development of life at large, form the subjects we propose 

 for treatment in the present paper. The inquiry, it may be 

 added, is one full of promise, especially if regarded as an in- 

 centive to a fuller and more complete study of the relations 

 of living beings to the world in which they live. 



No fishes are better known to ordinary readers than 

 the so-called " flat-fishes " the Pleuroneclida of the zoolo- 

 gist. Under this designation we include the soles, flounders, 

 halibut, turbot, brill, plaice (Figs. 59 and 60), and other less 

 familiar forms. As these fishes are observed on the fish- 

 monger's slab, or better still, when they are seen swimming 

 with a beautiful undulating motion of their bodies in our 

 great aquaria, the epithet " flat," as applied to their form, 

 would be regarded as of most appropriate kind. If an un- 



