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left ectetlimoid, to which the oblique eye mxiscles are attached, originally looked 

 outwards to the left; now it looks upward, and it has become increased in size. 

 Moreover, the left ectethnioid is still on the left side of the head, where it was 

 originally before the distortion commenced. Another important fact is tliat the 

 oblique muscles of ihe left eye are somewhat larger and stronger than those of the 

 right. 



These facts seem to me to have an important bearing on the question of the evolution 

 of the sole and other flat fishes, of the process by which the peculiar asymmetry which 

 characterises them was produced. All zoologists are evolutionists now, and it is 

 generally admitted that the flat fishes are descended from remote ancestors which 

 were symmetrical throughout their Yives. This is sufficiently evident from the fact 

 that all flat fishes when first hatched, and for some time afterwards, are at the 

 present day perfectly symmetrical. But two entirely opposite views are at present 

 held by different zoologists as to the process of evolution. One school of evolutionists 

 goes beyond Darwin in one direction, the other in another. The former school believe 

 that although the conditions of life and the habits of an individual animal do affect 

 its structure, modify it in various ways, these modifications are never inherited and 

 cannot therefore have anything to do with the process of evolution. All evolution 

 according to this view is due to the natural selection of variations which are an 

 advantage to the individuals in which they occur, and these variations are all due to 

 causes existing before the development of the individual. Such variations are called 

 congenital, and are inherited usually by the offspring of the ii'dividuals which 

 possess them, and usually develop to a still greater degree in the offspring of two 

 parents who both possessed them. These variations are entirely independent of 

 the habits or conditions or the use and disuse of organs. Such evolutionists explain 

 the distortion of the eyes in flat fishes in this way. A certain species of fish in remote 

 ages found it necessary to lie on the bottom ; among the individuals of this species 

 some had eyes which were very slightly asymmetrical, the lower eye being slightly 

 nearer the edge of the body than in the other individuals. Consequently these 

 individuals being able to see more than the others lived longest, escaped their 

 enemies, and left most offspring. As they bred together, and as variations again 

 occurred, some of these offspring had the lower eye still nearer to the edge of the 

 head, and these survived while the others perished, and so on, until in course of long 

 ages the present flat-fishes were produced. 



The other school of evolutionists believe that acquired characters are inherited to some 

 degree. It is admitted that the use of an organ enlarges it and improves it. and they 

 believe there is plenty of evidence tliat when the use of an organ in a particular manner 

 is continued generation after generation the modification is partly inherited in eacli 

 generation, and at last is wholly inherited. They hold therefore that tlie adaptations 

 of ori:rans to particular purposes, which are so conspicuous in animals and in plants, 

 are due to the use of the organs for those purposes, and, though the modification 



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