18 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



the science of embryology. It has been well called the 

 key to the laws of animal development, although, as a 

 science, almost created within the last half century. 

 Before then it was not known that animals, entirely 

 unlike one another when mature, might have almost 

 exactly similar beginnings. The metamorphoses of insects, 

 though so well known, are even more gradual than sup- 

 posed, and show us what wonderful changes of structure 

 can be effected during development. 



The life history of an individual animal in a remarkable 

 manner constitutes a sort of condensed epitome of its 

 descent, and in no case more so than that of man. 



Rudimentary organs, so common among man and 

 animals, are easily explainable upon the Darwinian 

 theory, but upon no other. The young whale, and also 

 the calf, have rudimentary teeth never destined to cut the 

 gums, because useless to them, but not so to their pro- 

 genitors. The snake has, in like manner, rudimentary 

 legs, never to be of service to it. Hosts of other examples 

 might be given. 



Use or disuse, Darwin thinks are important factors in 

 increasing or reducing organs when changed habits require 

 or no longer require them, and in this way natural selection 

 has an important influence, and is, as Darwin says, 

 "probably the main, though not the exclusive, means of 

 modification." 



" If, then," he sums up, " animals and plants do vary, 

 let it be ever so slightly and slowly, why should not 

 variations or individual differences, which are in any way 

 beneficial, be preserved and accumulated through natural 

 selection, or the survival of the fittest ? " 



" If man can, by patience, select variations useful to 

 him, why, under changing and complex conditions of life, 

 should not variations, useful to Nature's living products, 



