ANIMALS AND THEIR ENVIRONMENTS. 



233 



satisfy us that the paired fins are invariably 

 borne on the sides of these animals. This rule 

 of fish-structure accords with the position of the 

 limbs in all other vertebrate animals. These ap- 

 pendages are always paired, and are invariably 

 lateral in their position and attachments. We 

 are, therefore, forced to conclude that, unless the 

 flatfishes present extraordinary exceptions to the 

 laws of limb development and situation represent- 

 ed in all other vertebrate animals, they must, like 

 other fishes, carry their paired fins or limbs on 

 the sides of their bodies. Otherwise we must 

 assume that they bear the limbs on their backs 

 and on the lower surfaces of their bodies respec- 

 tively ; a supposition, the mere mention of which 

 is sufficient to show its absurd and erroneous na- 

 ture. It may thus be clearly shown that the flat 

 surfaces of the soles and their neighbors, judged 

 by the fact that they bear the paired fins, must 

 represent the sides of their bodies. And an ex- 

 amination of the other series of fins found in 

 these fishes would show the latter statement to 

 be correct. The second set of fins possessed by 

 fishes includes the so-called "unpaired" fins, 

 which are invariably situated in the middle line 

 of the body. With the "back " fins and "tail- 

 fin," as examples of these latter appendages, 

 every one is acquainted ; and when we look for 

 these fins in the flatfishes, we find them developed 

 in a very typical fashion. There is a long " back " 

 fin, for instance, fringing the body above, and de- 

 fining the back for us ; a second or " anal " fin 

 of equal extent borders the body below ; and the 

 tail-fin is equally well developed. An examina- 

 tion of the tail-fin alone would, in fact, show us 

 the true relationship of the various surfaces of 

 these fishes ; since in all fishes this fin is set ver- 

 tically, and not crosswise, as in the whales. Plac- 

 ing the tail-fin in its proper position, that is, set- 

 ting our flatfish with the back-fin uppermost, we 

 then note that the flat surfaces of the tail will 

 correspond with the flattened surfaces of the fish, 

 and that the latter must therefore be the sides of 

 the animal. 



But there still remain for comment and ex- 

 planation the remarkably-placed eyes, which, ac- 

 cording to our observations, are now seen to be 

 situated on one side of the body, and not on the 

 back, as is commonly supposed. The side on 

 which the eyes are placed is usually the left side ; 

 but in several species they are situated on the 

 opposite surface ; the eyed side being, as we have 

 seen, the dark-colored surface. To this latter 

 side, also, trfe mouth is to a large extent drawn, 

 this aperture thus becoming unsymmetrically 



developed. Occasionally, also, it may happen 

 that in species of flatfishes in which the eyes are 

 habitually situated on the left side, these organs 

 may be placed on the right, and vice versa. The 

 occurrence of this reversion of the eyes throws 

 some little light on the somewhat mechanical 

 causes and chance nature of the conditions which 

 determine the peculiar features and form of these 

 fishes. How have the eyes of these fishes come 

 to be developed on one side of the body ? and is 

 this condition original or acquired ? are questions 

 which the mere consideration of their peculiar 

 structure must suggest to the most casual observ- 

 er. It may be said that but two explanations are 

 open for acceptation in this, as in all other cases 

 relating to the development of life at large : 

 Either we may believe that the animals were 

 originally and specially created with these pecu- 

 liarities and abnormal features fully developed ; 

 or that these features are the result of secondary 

 laws and outward forces acting upon the form ; 

 and, through the form, determining the " way of 

 life " of the being, to use Goethe's expressive 

 phrase. The first hypothesis admits of no en- 

 largement or discussion. If accepted, it must be 

 treated as a matter of unquestioning faith around 

 which the mind may not attempt to travel. But 

 it is exactly this unquestioning belief in a theory 

 which the scientist will not recognize ; and more 

 especially, if from the other view of the matter 

 he gleans a large measure of aid in the attempt 

 to understand how the modifications before us 

 have been produced. Having due regard to the 

 alterations and changes of form and structure 

 that are so characteristic of living beings, and 

 recognizing the plasticity of life in all its aspects, 

 the zoologist will no more believe that the pecu- 

 liarities of the flatfishes present us with originally 

 created features, than that the deformities in man 

 which follow the accidents of human existence 

 are the products of a creative force of special 

 kind. 



That the case of the flatfishes has long formed 

 a text for grave biological discussion, is evident 

 from the attention it has received at the hands of 

 Mr. Spencer, Mr. St. George Mivart, and other nat- 

 uralists. Mr. Spencer, in dealing with the modifica- 

 tion of animal forms by the influence of external 

 conditions and environments, explains the want 

 of symmetry in the flatfishes by assuming that the 

 two surfaces of the body have been exposed to 

 different conditions. Respecting Mr. Spencer's 

 views, Mr. Mivart has remarked that " abundant 

 instances are brought forward by him of admira- 

 ble adaptations of structure to circumstances, but 



