132 BRITISH LIZARDS 



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 modified 

 in structure, in the direction of the reduction in size 

 of the limbs. These modifications " are hereditarily 

 transmitted, accumulated, and perfected with each 

 generation." The first lizards to have smaller limbs 

 transmitted them to their offspring ; the process con- 

 tinued ; 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 inter- 

 mediate condition. We may represent the process 

 diagrammatically thus : — 



{Male (long limb) f Male (short limb) T Male (limbless) 



have ofiFspring < have offspring < 



Female (long limb) I. Female (short limb) (^ Female (limbless), 



the structural change being due to — 

 (a) Action of the physical environment ; 

 (6) Hereditary transmission of these acquired 



characters ; 

 (c) Accumulation and perfection in succeeding 



generations. 



