1903 Reptile Studies 



o^j 



It is no part of our purpose to even mention the 

 various arguments for and against these opposing views, 

 every field naturalist can and should become acquainted 

 with them from zoological text-books. What we wish to 

 do is simply to take the case of the slow-worm as an 

 example of a species which has arisen as the result of 

 variation, and apply the two views to it. 



We may suppose that the ancient four-limbed lizard, 

 according to the first of the views enunciated, found itself 

 in the course of time, and in some circumstances of its 

 distribution, under the necessity of taking to a burrowing 

 life or living in loose sand, or in some other condition in 

 which the limbs were not well adapted for locomotion. 

 What the precise nature of the environment was does not 

 matter. Whatever it was, " the organisms are profoundly 

 modified by the necessities of their existence, and the 

 nature of their physical environment." That is to say, 

 that this lizard, because of this environment, became modi- 

 fied in structure, in the direction of the reduction in size 

 of the limbs. These modifications " are hereditarily trans- 

 mitted, accumulated, and perfected with each generation." 

 The first lizards to have smaller limbs transmitted them 

 to their offspring ; the process continued ; they in their 

 turn were still further modified in the same direction, and 

 transmitted their still smaller limbs to their offspring. 

 The process is " perfected with each generation," until, 

 finally, as the result of the effect of their environment, 

 the lizard has no external limbs left at all. Thus a new 

 species of lizard has arisen, without limbs, and at the same 

 time some may be still in a transitional stage, with small 

 limbs, or the hind pair only, showing the intermediate condi- 

 tion. We may represent the process diagrammatically thus: — 



( Male (long limb) ( Male (short limb) /-Male (limbless) 



have offspring - have offspring \ 



y Female (long limb) I Female (short limb) I Female limbless), 



the structural change being due to — 



{a) Action of the physical environment ; 



(b) Hereditary transmission of these acquired characters; 



(c) Accumulation and perfection in succeeding gener- 



ations. 



