THE DEVELOPMENT OF THE FROG'S EGG 333 



Effect of Heat and Light on Development. Eggs devel- 

 oping in normal environments in nature arrive at nearly 

 the same end-result even when the environments are not 



FIG. 306. A chart showing the correlation between the stage of development 

 of the frog on successive days and the temperature at which it has de- 

 veloped. From Higgenbottom. 



identical. We gain, in consequence, an impression that 

 development proceeds unaffected by any changes in the 

 outside world. But this is not true. For one thing, the 



