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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



in the immense majority of these instances it is 

 very difficult, if not impossible, to see how exter- 

 nal conditions can have produced or even have 

 tended to produce them. For example," he con- 

 tinues, " 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 corre- 

 lation which all must admit to exist between the 

 forms of organisms and their surrounding exter- 

 nal 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 inci- 

 dent forces must act upon them and upon non- 

 living aggregations of matter in the 6ame way 

 and with similar effects." These quotations will 

 serve to show that zoological authority has recog- 

 nized, in the case of the flatfishes, an important sub- 

 ject of remark. With reference to the latter por- 

 tion 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 mo- 

 ment doubt the influence of those forces — summed 

 up in the words "life" and "vital" action — nor 

 does Mr. Spencer, as far as I can learn, ignore 

 their existence. It is the life and internal forces 

 of the living being which present us with the pri- 

 mary conditions of existence. What we do con- 

 tend 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 flatfishes. 



The first point in their history to which atten- 

 tion may be directed is that in their early life, and 

 when the young fish emerges from the egg, the 

 eyes are situated where we should naturally expect 

 to find these organs — one on each side of the 

 head. Moreover, in the days of its youth the flat- 

 fish is thoroughly symmetrical in all other respects 

 even to the coloration of its body, the two sides 

 being tinted of the same light hue. Soon, how- 

 ever, a change of structure and conformation be- 

 gins to be apparent, especially in the head-region. 

 The eye of the lower side, on which the fish is des- 

 tined to rest, begins literally to travel round to 

 the upper side of the body ; this process taking 

 place merely through a curious malformation and 

 twisting of the bones of the head, and not by 



means of the eye passing through the skull, as was 

 formerly supposed. Then also the color of the 

 upper side of the body gradually deepens and ac- 

 quires the tint of adult life ; a hue admirably in 

 harmony with the surrounding sand, and rendering 

 the detection of these fishes as they rest on the 

 sandy sea-bed a matter of extreme difficulty, as 

 any one who has " speared " flounders knows. 

 The causes of the development of color on the up. 

 per surface may doubtless, as Darwin remarks, be 

 attributed to the action of light ; but it is nota- 

 ble that in some flatfishes there exists a chame- 

 leon-like power of altering the tint of their bodies 

 so as to bring them into harmony with the partic. 

 ular color of their surroundings. The acquirement 

 of this latter condition becomes allied to that 

 termed " mimicry ; " but to explain the develop- 

 ment of the power of changing color, we must 

 call to aid conditions other than that of the action 

 of light, and which affect and influence the more 

 intricate and hidden forces of living beings. 

 Thus are gradually acquired the peculiar feat- 

 ures which mark the adult existence of these 

 fishes. The chronicle of their early life and his- 

 tory impresses one fact primarily on our minds, 

 namely, that if their development is to be held as 

 furnishing a clew to the origin of their modifica- 

 tions, the knowledge that at first the flatfishes 

 possess symmetrical bodies demonstrates that 

 originally they exhibited, as adults, no modifi- 

 cation or deformity such as they now possess. 

 Assume with Darwin — and the assumption is both 

 reasonable and warranted — that the "embryonal 

 (or young) state of each species reproduces more 

 or less completely the form and structure of its 

 less modified progenitors," and we may be taught 

 by the development of the flatfishes that they 

 have sprung from ancestors which possessed sym- 

 metrical bodies, and that the conditions they pre- 

 sent to our notice have certainly been of acquired 

 nature. 



But the question, " How have these abnor- 

 mal conditions and modifications of structure 

 been acquired ? " still remains for consideration. 

 It is on this point that Mr. Mivart challenges the 

 adequacy of external conditions and outward in- 

 fluences to produce the characteristic deformities 

 before us. On another occasion this author re- 

 marks : " If this condition had appeared at once, 

 if in the, hypothetically common ancestor of 

 these fishes an eye had suddenly become trans- 

 ferred, then the perpetuation of such a transforma- 

 tion by the action of ' Natural Selection ' is con- 

 ceivable enough. Sudden changes, kowever, are 

 not those favored by the Darwinian theory, and, 



