Family and Society 



egg may have a diameter ten times as great as 

 that of a certain fish; It should contain one thou- 

 sand times as much material. The egg of a bird 

 contains from one hundred to one thousand times 

 as much food as a frog's egg. 



If the amount of material which the animal 

 can put Into eggs Is rapidly diminishing, and the 

 amount required for every egg Is Increasing, the 

 number of eggs must be lessening rapidly. We 

 may say roughly that for every egg produced by 

 a bird, the reptile produces ten, the frog fifty or 

 more, and fishes from one hundred to ten thou- 

 sand. 



This diminution in the number of eggs, while 

 unavoidable. Is a very serious danger to the sur- 

 vival of the species. It greatly diminishes the 

 chances of favorable variations. If It goes too 

 far, the number of Individuals In successive gen- 

 erations win steadily diminish until the species 

 becomes extinct. The fish can survive even If 

 a large share of Its eggs are eaten by other ani- 

 mals; not so the bird or mammal. Every egg 

 Is of great value. Eggs and young must be 

 guarded and cared for. Hence the nesting hab- 

 its of birds and the Intrauterine development of 

 all mammals except the very lowest are a physlo- 



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