232 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



And the rarest form mysteriously preserves the 



primitive type. 

 Form, therefore, determines the animal's way of 



life, 

 And in tnrn the way of life powerfully reacts upon 



all form. % 



Thus the orderly growth of form is seen to hold, 

 While yielding to change from externally-acting 



causes." 



Elsewhere, Goethe says of this subject, that 

 while " an inner original community forms the 

 foundation of all organization, the variety of 

 forms, on the other hand, arises from the neces- 

 sary relations to the outer world ; and we may, 

 therefore, justly assume an original difference of 

 conditions, together with an uninterruptedly pro- 

 gressive transformation, in order to be able to 

 comprehend the constancy as well as the varia- 

 tions of the phenomena of form." 



Thus are clearly expressed Goethe's views that 

 the living form was a mobile quantity, influenced 

 and altered to a greater or less degree by out- 

 ward causes, acting in concert with the internal 

 life-forces, and inherited constitution of the being ; 

 in other words, with regard to the form of ani- 

 mals and to borrow Shakespeare's phrase, we 

 might say : 



" In them Nature's copy's not eterne." 

 Later years brought to biology the enriching 

 knowledge of Darwin ; and generalizations regard- 

 ing the origin of living beings, startling and rev- 

 olutionizing in their nature, were submitted to 

 the scrutiny of the scientific world. But, after 

 the first feelings of surprise had passed away, 

 and as the clearness of Darwin's views and their 

 exceeding harmony with the facts of life were ob- 

 served, biologists gladly hailed his generaliza- 

 tions as affording the basis of a reasonable con- 

 ception of Nature at large. Facts in animal life, 

 hitherto regarded as simply inexplicable, and 

 which were accepted as primary mysteries of 

 biological faith, received at the hands of Darwin 

 new and rational explanations ; and to the emi- 

 nently plain and consistent nature of the ideas 

 involved in his system of thought may be as- 

 cribed the great success and ready acceptation 

 which evolution has met in the world of thought 

 at large. Among other features which this meth- 

 od of thought exhibits in characteristic fashion, 

 is that of assigning a paramount place to the 

 influence of habit and use and of outward cir- 

 cumstances upon the form and " way of life " of 

 living beings. A few illustrations of the changes 

 which both common and unwonted circumstances 

 of existence may effect in the history of ani- 

 mals, together with a brief chronicle of the in- 



fluence of such changes on the development of 

 life at large, form the subjects we propose for 

 treatment in the present paper. The inquiry, it 

 may be added, is one full of promise, especially 

 if regarded as an incentive to a fuller and more 

 complete study of the relations of living beings 

 to the world in which they live. 



No fishes are better known to ordinary read- 

 ers than the so-called " Flatfishes " — the Pleuro- 

 nectidce of the zoologist. Under this designation 

 we include the soles, flounders, halibut, turbot, 

 brill, plaice, and other less familiar forms. As 

 these fishes are observed on the fish-monger's 

 slab, or, better still, when they are seen swim- 

 ming with a beautiful undulating motion of their 

 bodies in our great aquaria, the epithet "flat," 

 as applied to their form, would be regarded as of 

 most appropriate kind. If an unscientific ob- 

 server were asked which surfaces were flattened 

 in these fishes, he would be very apt to reply that 

 the one flat surface was the back, and the other 

 the belly of the animal. In proof of the cor- 

 rectness of his assertion, he might point to the 

 well-known fact that one surface — the so-called 

 " back " — is dark-colored, while the opposite and 

 presumed under surface is white. Again, the 

 idea that the darker surface is the back would 

 be strengthened by the observation that it bears 

 the eyes, and further that the fish swims with 

 this surface uppermost. Notwithstanding these 

 apparently well-founded observations, however, 

 the zoologist finds ample reason for a complete 

 denial of their validity and correctness. He 

 would first direct attention to the fact that, on 

 each flat surface of the fish, and in the breast- 

 region, a certain fin is to be discerned. These 

 fins form a pair, possessed by all save the very 

 lowest fishes; they are named "pectoral" or 

 " breast fins," and correspond, as may be proved 

 by an examination of their skeleton, with the 

 fore-limbs of other vertebrate animals. In the 

 flatfishes, it usually happens that one pectoral fin 

 is of smaller size than the other. Moreover, 

 there are other two fins, also paired, to be dis- 

 cerned in these fishes, placed below the breast- 

 fins, one on each flat surface of the body, but ex- 

 hibiting a somewhat rudimentary structure and 

 only a slight development as compared with their 

 representatives in other fishes. These latter are 

 the two " central " fins of the zoologist, and an 

 examination of their skeleton and nature shows 

 that in reality they represent the hind-limbs of 

 the fish, just as the breast-fins correspond to the 

 fore-members. A very cursory examination of 

 other fishes in which both sets of fius exist would 



