Preface to the Seventh Edition. 



The book has been enlarged by the addition of a chapter 

 on the rehition of animals to their surroundings, on varia- 

 tion, and the factors of organic evolution, as well as a brief 

 chapter on heredity. It is believed that the attention of 

 pupils should be called to tlie wonderful harmony and 

 adaptation in nature, and to the apparent causes of such rela- 

 tions; and that they should be led to observe for themselves, 

 wliere possible, examples of adaptation in common shells, 

 insects, birds, etc. Suitable collections can be made for 

 this purpose and exhibited or examined in the classi'oom. 



A number of corrections have been made, the most 

 important change being in the position of the Echino- 

 derms, which are placed after the Vermes. 



PuoviDENCB, R. I,, July 15, 1897. 



