Lect. VI.] SIGNS OF TRANSFORMATION. 165 



waifs or strays from almost extinct groups that could 

 not make their one talent ten. 



We are unable, without strong effort, to imagine 

 what may l)e done l)y slow changes, through countless 

 thousands of years ; moreover, nature has not left 

 herself without a witness as to what she can accomplish, 

 rapidly, at times, when changes come suddenly upon 

 living creatures. I am of opinion that too much has 

 been made of slow, almost infinitesimal changes, taking- 

 place during long secular periods ; nature has, in the 

 morphological force, in relation to various surroundings, 

 an unused surplusage of modifying energy that is practi- 

 cally'infinite. Hitherto, metamorphosis has been mainly 

 known in the Arthropods — insects and their relations — 

 but we are waking up to the importance of this l3rancli 

 of our subject in the study of the Vertebrata ; tliere are 

 creatures, and not a few of them, who show us what the 

 constructive energies of a living creature can do in a 

 single life term. Everywhere, also, in the develojDment 

 from the embryo of each high type, we see the foot- 

 }trints or marks of the most marvellous transforma- 

 tions that took lAace in the green youth-time of 

 tlie earth. 



