306 LEISURE-TIME STUDIES. 



conditions and environments, explains the want of symmetry 

 in the flat-fishes by assuming that the two surfaces of the 

 body have been exposed to different conditions. Respect- 

 ing Mr. Spencer's views, Mr. Mivart has remarked, that 

 " Abundant instances are brought forward by him of admir- 

 able adaptations of structure to circumstances, but in the 

 immense majority of these instances it is very difficult, if 

 not impossible, to see how external conditions can have 

 produced or even have tended to produce them. For 

 example," he continues, " we may take the migration of an 

 eye of the sole from one side of the head to the other. 

 What is there here either in the darkness, or the friction, 

 or in any other conceivable external cause, to have produced 

 the first beginning of such an unprecedented displacement 

 of the eye? Mr. Spencer has beautifully illustrated that 

 correlation which all must admit to exist between the forms 

 of organisms and their surrounding external conditions, but 

 by no means proved that the latter are the cause of the 

 former. Some internal conditions," concludes the author, 

 " (or in ordinary language some internal power and force) 

 must be conceded to living organisms, otherwise incident 

 forces must act upon them and upon non-living aggregations 

 of matter in the same way and with similar effects." These 

 quotations will serve to show that zoological authority has 

 recognised, in the case of the flat-fishes, an important subject 

 of remark. With reference to the latter portion of Mr. 

 Mivart's observations regarding the power and presence of 

 internal forces in animals, it may be said that no naturalist 

 may for a moment doubt the influence of those forces 

 summed up in the words " life " and " vital action " nor does 

 Mr. Spencer, so far as I can learn, ignore their existence. 

 It is the life and internal forces of the living being which 

 present us with the primary conditions of existence. What 

 we do contend for, however, is that outward circumstances 

 powerfully influence these internal forces, and through such 

 influence produce modifications both of form and structure 

 in living beings. In support of this latter opinion, no animals 

 furnish more satisfactory evidence than the flat-fishes. 



