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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



cided deformity, and induces the twisting of the 

 bones of the head. So that, in response to the 

 frequent efforts of the young fish, the lower eye 

 is gradually transposed to the side of the body 

 which will hereafter be the uppermost surface, 

 and which will meanwhile have been acquiring 

 its characteristic coloration. Such is the expla- 

 nation given by competent observers of the man- 

 ner in which the flatfishes have acquired their 

 strange modifications of structure. The flatfishes 

 of to-day acquire this modification in virtue of in- 

 herited tendencies, and of the effect of habit trans- 

 mitted through many antecedent generations. But 

 the observation of the stages through which the 

 young animals pass in the seas of to-day, reveals 

 a truthful and unerring history of the fashion in 

 which their far-back progenitors inaugurated the 

 first phases in their singular transformations. 



So far as the explanation of the curious feat- 

 ures presented by the flatfishes goes, it is fully 

 supported by facts as they stand. Additional 

 evidence of weighty kind, however, is obtainable 

 from various sources in favor of Goethe's asser- 

 tion that form of body " determines the animal's 

 way of life," and that " in turn the way of life 

 powerfully reacts upon all form." The evidence 

 that the deformity in question has been acquired 

 through the material contact of surroundings with 

 the bodies of the first flatfishes is derived from 

 a twofold source — firstly, from a view of the va- 

 rious members included in the group of the flat- 

 fishes ; and, secondly, from our knowledge of the 

 development of abnormal features in other fishes 

 and in other groups of animals. It would cer- 

 tainly afford some ground for Mr. Mivart's remark, 

 that by "Natural Selection" we might require to 

 postulate the sudden transference of the lower 

 eye to the upper side of the head, if the flatfishes 

 were found to present a thorough uniformity and 

 similarity in their deformity. If the whole race 

 or family of these fishes, without a single excep- 

 tion, presented the malformations in a typical de- 

 gree, then the idea of sudden and sharp modifi- 

 cation might be rendered probable enough. But 

 the systematic naturalist would inform us that 

 these fishes are not uniformly modified. On the 

 contrary, they present us with a varied array of 

 forms, at the one extremity of which we meet 

 with symmetrical flatfishes, having eyes entirely 

 unaltered in position, possessing equal-sized fins, 

 and retaining their young or embryonic charac- 

 ters ; while at the other extremity of the group 

 we observe fishes in which the deformities obtain 

 their highest development. Thus there is a genus 

 of flatfishes known as Hippoglossus, and which 



includes the various specie- of halibut. Some 

 species of this group— such as Hippoglossus pin- 

 ffuis — retain throughout life the characters, form, 

 and symmetry, they present on leaving the egg. 

 From this unaltered and undeformed species of 

 flatfishes we may pass by easy and gradual tran- 

 sitions to such fishes as the soles, in which the 

 distortion reaches a very typical development. 

 In this fact of the varying degrees of abnormality 

 exhibited by these fishes, we may find a counter- 

 proof of the acquirement of these peculiar feat- 

 ures. 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 

 conditions have been not merely acquired, but 

 that they have been favored in some species to 

 the neglect or escape of others. In the Hippo- 

 glossi we may see representatives of the original 

 type from which the modern flatfishes 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 overbalancing them- 

 selves — and from thus being placed in a false 

 position, as it were, have gradually adapted them- 

 selves, through a curious modification of form, to 

 a new " way of life." 



A second series of facts corroborative of the 

 view that the flatfishes 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 ani- 

 mals. Mr. Darwin mentions the curious fact of 

 human history, authenticated by surgical expe- 

 rience, that " in young persons whose heads from 

 disease have become fixed either sideways or 

 backways, one of the eyes has changed its posi- 

 tion and the bones of the skull have become 

 modified." So also, if one ear of a lop-eared rab- 

 bit tends to fall downward and forward, its mere 

 weight is found to affect the development and 

 growth of all the bones of the skull, and to cause 

 a forward protrusion of the head on that particu- 

 lar side. Mechanical causes, and the mere action 

 of weight or strain, may thus produce changes 

 of surprising extent in structures of greater firm- 

 ness than the soft skulls of fishes. The evi- 

 dence in support of the evolutionist's theory of 

 flatfish modification, however, is also strength- 

 ened by certain cases of distortion which follows 

 upon the habit evinced by the young of certain 

 well-known and symmetrical fishes of resting on 

 one side. Young trout, salmon, and perch, have 



