EVOLUTION AND ITS CONSEQUENCES. 13 



this head may be discussed the natural selection of Wallace and 

 Darwin and other propositions of similar import. 



'^ Retardation " continued terminates in extinction. Examples 

 of this result are common ; among the best known are those of 

 the atrophy of the organs of sight in animals inhabiting caves. It 

 is asserted that the young of both the blind crawfish {Orcoiiedes 

 pellucidus) and the lesser blind fish [TyphlicMliys suhterraneus) 

 of the Mammoth Cave possess eyes. If these statements be accu- 

 rate, we have here an example of what is known to occur else- 

 where, for instance, in the whalebone whales. In a foetal stage 

 these animals i30ssess rudimental teeth like those of many other 

 Cetacea when adult, which are subsequently absorbed. So also 

 with the foetal ox ; the upper incisor teeth appear in a rudimental 

 condition, but are very early removed. The disappearance of the 

 eyes is regarded by Dr. Packard, with reason, as evidence of the 

 descent of the blind forms from those with visual organs. I would 

 suggest that the process of reduction illustrates the law of *^ re- 

 tardation " accompanied by another phenomenon. Where charac- 

 ters which appear latest in embryonic history are lost, we have 

 simple retardation, that is, the animal in successive generations 

 fails to grow up to the highest point of completion, falling farther 

 and farther back, thus presenting an increasingly slower growth 

 in the special direction in question. Where, as in the presence of 

 eyes, we have a character early assumed in embryonic life, retarda- 

 tion presents a somewliat different phase. Each successive genera- 

 tion, it is true, fails to come up to the completeness of its prede- 

 cessor at maturity, and thus exhibits ^^retardation," but this 

 process of reduction of rate of growth is followed by its termina- 

 tion in the part long before growth has ceased in other organs. 

 This is an exaggeration of retardation, and means the early termi- 

 nation of the process of force-conversion, which has been previ- 

 ously diminishing steadily in activity. 



Thus the eyes of the Orconectes probably exhibited for a time 

 at maturity the incomplete character now found in the young, a 

 retarded growth continuing to adult age, before the termination 

 of growth was withdrawn by degrees to earlier stages. With this 

 early termination of growth came the phase of atrophy, the in- 

 complete organ being removed and its materials transferred to 

 other parts through the greater activity of '' growth-force." Thus, 

 for the reduction of organs, we have ''retardation " ; but for their 

 extinction, ''retardation and atrophy." 



