230 ANIMAL PEDIGREES 



closely corresponding with that in which it first 

 appears in the dogfish, and a curious point about it 

 is that in the frog the oesophagus becomes solid just 

 before the mouth opening is formed, and remains 

 solid for some little time after this important event. 

 This closing of the oesophagus clearly cannot be 

 recapitulation, but the fact that it occurs at corre- 

 sponding periods in the frog and the dogfish 

 suggests that it may possibly, as Balfour hinted, 

 "turn out to have some unsuspected morphological 

 bearing." 



A matter which at present is attracting much 

 attention is the question of degeneration. Natural 

 selection, though consistent with and capable of 

 leading to steady upward progress and improvement, 

 by no means involves such progress as a necessary 

 consequence. All it says is that those animals will 

 in each generation have the best chance of survival 

 which are most in harmony with their environment, 

 and such animals will not necessarily be those 

 which are ideally the best or most perfect. 



If you go into a shop to purchase an umbrella 

 the one you select is by no means necessarily that 

 which most nearly approaches ideal perfection, 

 but the one which best hits off the mean between 

 your idea of what an umbrella should be and the 

 amount of money you are prepared to give for it ; 

 the one in fact that is on the whole best suited to 

 the circumstances of the case, or the environment 

 for the time being. It might well happen that you 

 had a violent antipathy to a crooked handle, or else 

 were determined to have a catch of a particular kind 



