212 



THE THEORY OF EVOLUTION 



second laying period yields us, however, five to twelve 

 eggs, which are enveloped in a parchment- like, yellowish- 

 white, opaque shell, like those which other Lizards 

 possess/ l 



With the Meadow Lizard (L. serapa) Kammerer has 



established the fact that the 

 normally parchment-like eggs 

 become quite hard-shelled (and 

 at the same time round) if the 

 parents are kept permanently 

 under a temperature of 30 to 

 35 C. (Fig. 46). If the lizards 

 be restored to the normal 

 cooler conditions, the first 

 generation lays still hard- 

 shelled eggs ; and also the 

 young which are born under 

 normal conditions from the 

 c heat forms/ which have be- 

 come black by reason of the 

 warmth, still clearly show the 

 black coloration in the first 

 generations and, quite natur- 

 ally, the more so the nearer 

 they approach the adult form. The very first stages 

 show still clearly the lighter colouring. 



This example confirms in all points what we have 

 so far said regarding the influence of the external world 

 and the influencing of the embryonic stages ; it shows 



1 ' Other ' = normal egg-laying forms. 



c d 



FIG. 46. THERMAL CHANGES 



IN THE MEADOW LIZARD. 

 a, normal animal ; b, artificially 

 blackened; c, normal egg; d, 

 egg of first deposit in heat ; e, 

 hard-shelled egg ex second and 

 third laying periods. 



(After Kammerer.} 



