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. 



