84 MAN, THE ANIMAL 



later In the growth of the embryo are transformed 

 into the skin. In the mature condition of the 

 nervous system, surrounded as it is by a definite 

 number of bones in the skull, no one would think 

 of suggesting that it is derived from cells like 

 those that form the skin, unless he knew of these 

 clearly defined changes. 



Soon after this, the embryo has a long tail and 

 gills for breathing. But it does not look like its 

 parents except In a very general way. It Is now In 

 the tadpole stage which lasts for nearly two years, 

 after which the body becomes like the parent. 

 (Figs. 26 G-K-L, 27.) 



In many of the details, the facts mentioned In 

 the development of this salamander are similar in 

 all animals with a backbone; In the stages shown 

 In Figs. 26 A-B-G-H, the changes are similar to 

 corresponding stages in all animals. On the other 

 hand, so distinctive are the embryonic changes, 

 that one has no difficulty in distinguishing the em- 

 bryos of the fish, the frog, the reptile, or man. 

 There Is an individualistic feature in the minute 

 changes In development that is characteristic of 

 each species. 



Summary 



During the past twenty-five years scientists have 

 accumulated a vast amount of Information about 

 the embryology of animals and plants. They 

 have come to know the order in which events 



