184 THE POPULAR SCIENCE MONTHLY. 



point is gained in explanation of the modus operandi of the process." 

 He then proceeds to point out a number of related genera in which 

 the external ones present eyes, while the cave forms are blind. As to 

 variability, he cites the blind siluroid fish from Conestoga, Pennsyl- 

 vania, showing that, while all of several specimens were blind, the 

 degree of atrophy was marked not only in different fishes, but even on 

 different sides of the same fish. In some the corium was perforate, 

 in others it was imperforate. In some the ball of the eye was oval, 

 in others collapsed. 



We have in the meagre fauna of the caves convincing proof of the 

 gradual undoing of parts so to speak on the withdrawal of influ- 

 ences favorable to them ; even so exquisite a structure as the eye as 

 a result of selection almost inconceivable, yet not only becoming 

 rudimentary, but almost disappearing, by the withdrawal .of those 

 influences which were in part conducive to its building up. So dis- 

 tinct are these undoing stages that, were we sure of the stable vari- 

 ability of all of them, we could with certainty indicate the relative 

 age of each cave inhabitant. 



Prof. Alpheus Hyatt and Prof. E. D. Cope almost simultaneously 

 established a number of propositions relating to certain large groups 

 of animals which had never been recognized before. The theory of 

 acceleration and retardation in which certain groups acquire rapidly 

 new characters, while corresponding groups acquire the same charac- 

 ters more slowly, forms a portion of the theory of these naturalists. 

 Prof. Hyatt has shown among Ammonites a parallel between the 

 life-stages of. the individual and similar stages in the group based 

 upon an examination of suites of specimens as studied by him in 

 Europe and America. It is utterly impossible to do the slightest 

 justice to the thoroughly original views of these gentlemen without 

 the aid of explanatory diagrams. While reluctantly abandoning the 

 attempt, I must at the same time express the regret that neither of 

 these investigators has seen fit to present to the public an illustrated 

 and simple outline of the main features of their theories and the facts : 

 Prof. Cope basing in part his propositions on groups of animals, many 

 of which comprise fossil forms brought to light in the West, of which 

 but few restorations have yet been made ; and Prof. Hyatt basing his 

 work on fossil Ammonites from the Jurassic and adjacent beds of 

 Europe, of which but one complete collection is to be found in this 

 country. 



Surely, with this unfamiliar material, an excuse may be offered in 

 not attempting a popular presentation of propositions and laws, some 

 doctrinal and others theoretical, which must yet be looked upon as 

 profound and permanent additions to the philosophy of evolution. A 

 reference may be made to Prof. Cope's essays, entitled " Origin of 

 Genera," " On the Method of Creation of Organic Types," " Con- 

 sciousness in Evolution," " On the Theory of Evolution," and numer- 



