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THE POPULAR SCIENCE MONTHLY, 



CORRESPONDENCE. 



TO WHAT EXTENT IS EVOLUTION 

 YISIBLEf 



To the Editor of the Popular Science Monthly : 



"It is less unphilosophical to suppose 

 that each species has been evolved from a 

 predecessor by a modification of its parts, 

 than that it has suddenly started into ex- 

 istence out of nothing. Nor is there much 

 weight in the remark that no man has ever 

 witnessed such a transformation taking 

 place." (Draper, " History of the Conflict 

 between Religion and Science," p. 192. 

 "International Scientific Series," No. 12.) 



There stands, in a window of my wife's 

 sitting-room, a potted slip of geranium. 

 To-day, I heard her remark, " I can see that 

 this grows now, every day." In what sense 

 is this true ? By remembering its size and 

 condition of yesterday, and comparing it 

 with its present dimensions and conditions, 

 an increase and change are demonstrable. 

 It certainly has grown. But, if we were to 

 sit down at sunrise and watch unceasingly 

 until sunset, or by lamplight continue the 

 vigil until sunrise again, we would in all this 

 time have seen no enlargement of the main 

 stem no unfolding of a leaf-bud ; still, both 

 these changes have taken place within 

 twenty-four hours, and, of course, in full 

 view. 



Is it not true in the same way, but far 

 less rapidly, that the changes in animal life 

 are constantly occurring so gradually, that 

 we cannot mark and measure the prog- 

 ress, but, like the plant, can appreciate the 

 changes when considerably advanced ? Tlie 

 birds, the fishes, the insects of to-day are the 

 same that our grandparents knew. Linnaeus 

 would recognize our white-headed eagle, if 

 he could see one now ; yet, in truth, they 

 are not wholly the same. Just as we will 

 realize, in the coming May, a great change 

 in the forest-trees, then clothed in verdure, 

 and now bare and seemingly lifeless, will 

 not, in the life-giving spring of a coming 

 geon, the changes not now discernible be 

 seen, admired, and studied, by the people 



of that time? Taking up some of the 

 more familiar objects about me, I have en- 

 deavored to see if there was not a possibil- 

 ity of detecting some trace of changes now 

 in progress, reminding one of the changes 

 of a growing plant. 



The change now in progress in any spe- 

 cies, say of fishes, is to become, if I am 

 correct in my surmise, visible in fifty centu- 

 ries or more. From what we can now learn 

 of the fish, can we determine the direction 

 of the change ; can we predict its charac- 

 ter? Our slip of geranium has to-day a 

 small outgrowth at one side of the stem ; 

 elsewhere the bark is smooth and unbroken. 

 If, by the microscope's aid, we study the 

 character of the structure of the main stem, 

 if we learn every detail of the physiology 

 of the plant, we conclude that it is a living, 

 healthy organism, not depending upon the 

 leaf-bud. As a mere bud, it is not a neces- 

 sity ; but, as a full-blown leaf, it is. If, now, 

 we carefully study the habits of any of our 

 common fishes, we will find in them certain 

 peculiar habits, which may be compared to 

 the leaf-bud ; and I believe these habits, in 

 many cases, are only faint traces of a com- 

 ing change that will expand like the open- 

 ing leaf-bud, into a fully-established char- 

 acteristic in the far-distant to-morrow of a 

 coming age. 



In this way to this extent is not evo- 

 lution visible ? 



As an example, let me call your atten- 

 tion to our well-known mud-minnow {Mela- 

 nura Umi). This fish I have very carefully 

 studied for several years, and s-eldom fail 

 to see something peculiar in its habits, 

 every additional hour I spend in watching 

 them, whether in an aquarium or their na- 

 tive haunts. On observing the movements 

 of some remarkably large specimens lately, 

 in an aquarium, I was forcibly struck with 

 the pecuhar use they made of their pectoral 

 fins. These fins, in most fishes, are kept 

 parallel, or nearly so, with the body, and 

 are usually thin, transparent, and with very 

 flexible rays. These conditions, which vary 



