20 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



3. Parallelism. This states that all organisms in 

 their embryonic and later growth pass through stages 

 which recapitulate the successive permanent condi- 

 tions of their ancestry. Hence those which traverse 

 fewer stages resemble or are parallel with the young of 

 those which traverse more numerous stages. This is 

 the broad statement, and is qualified by the details. 



4. Teleology.- -This is the law of fitness of structures 

 for their special uses, and it expresses broadly the 

 general adaptations of an animal to its home and 

 habits. 



The first and fourth of the laws above enumerated 

 are taken for granted as generally accepted, and are 

 not especially considered in the following pages. The 

 second law, that of successional relation, is discussed 

 and illustrated under the two heads of Variation and 

 Phylogeny; the first expressing contemporary relations, 

 and the second, successive relations in time. The third 

 law, or that of parallelism, is considered in a chapter 

 devoted to that subject. 



