INTRODUCTION. I $. 



gradual transformation of an egg into a tadpole. As far as a 

 certain stage the process or progress is the same in all eggs, 

 whether of birds, fishes, or reptiles ; but we will reserve the 

 examination of the frog embryos for the present. Enough has 

 been said in this already lengthened Introduction to the Verte- 

 brates. 



