REVISER'S NOTE. 



IN this revision of Professor Orton's work only such 

 changes have been introduced into the text as have been 

 made necessary by recent progress in Zoology. Some 

 errors of statement have been corrected, and the classifica- 

 tion has been slightly changed. The principal addition 

 consists of an Appendix composed of directions and sug- 

 gestions for the performance of simple physiological ex- 

 periments, and for the examination of certain animals 

 representative of the more important groups. These ex- 

 periments and dissections are so elementary that they may 

 easily be performed by either teacher or pupil. Yery 

 little apparatus, few instruments, and no special skill are 

 required. The Appendix is designed to make the book of 

 more practical value than formerly, and thus adapt it to 

 the labwatory rather than the literary method of teach- 

 ing. 



An asterisk at the head of the chapter indicates that its 

 subject-matter may be illustrated by practical work, for 

 which directions will be found in the Appendix. 



CHAKLES WEIGHT DODGE. 



UNIVERSITY OF ROCHESTER 



