3 I2 LEISURE-TIME STUDIES. 



the contrary, they present us with a varied array of forms, 

 at the one extremity of which we meet with symmetrical 

 flat-fishes, having eyes entirely unaltered in position, possess- 

 ing equal-sized fins, and retaining their young or embryonic 

 characters ; whilst at the other extremity of the group we 

 observe fishes in which the deformities obtain their highest 

 development Thus there is a genus of flat-fishes known as 

 Hippoglossus (see Fig. 60), and which includes the various 

 species of halibut. Some species of this group such as 

 Hippoglossus pinguis retain throughout life the characters, 

 form, and symmetry they present on leaving the egg. From 

 this unaltered and undeformed species of flat-fishes we may 

 pass by easy and gradual transitions to such fishes as the 

 soles, in which the distortion reaches a very typical develop- 

 ment. In this fact of the varying degrees of abnormality 

 exhibited by these fishes, we may find a counterproof of the 

 acquirement of these peculiar features. A creative act or a 

 sudden modification would have affected the entire race. A 

 graduated series of forms, exhibiting every degree and stage 

 of abnormal development, shows that the distorted condi- 

 tions have been not merely acquired, but that they have 

 been favoured in some species to the neglect or escape of 

 others. In the hippoglossi we may see representatives of 

 the original type from which the modern flat-fishes have been 

 evolved; and we may conceive of this evolution having 

 taken place through the laws of ordinary development acting 

 upon bodies, which, from a mechanical cause that of over- 

 balancing themselves and from thus being placed in a false 

 position, as it were, have gradually adapted themselves, 

 through a curious modification of form, to a new "way of life." 

 A second series of facts corroborative of the view that 

 the flat-fishes have thus evolved their peculiar features by 

 adaptation to the outward circumstances of their existence, 

 is furnished by a knowledge of the distortions which follow 

 upon unusual modes of life or accident in other animals. 

 Mr. Darwin mentions the curious fact of human history, 

 authenticated by surgical experience, that " in young persons 



