434 ANIMAL STUDIES 



statement is only true when stated very broadly, for there 

 are many exceptions or modifications. The embryonic or 

 larval animal is subject to almost endless secondary changes 

 and adaptations whenever these changes are for the advan- 

 tage of the animal. In general, the simpler the structure 

 of the animal and the less varied its relations in life, the 

 more perfectly are these ancient phases of heredity pre- 

 served in the process of development. In such case, the 

 more perfect the parallelism between the development of 

 the individual and the succession of forms in geologic time. 



