312 AN INTRODUCTION TO ZOOLOGY. 



ever, if the work involves learning the use of the 

 miscroscope for the first time, the course is long and 

 tedious, even with the assistance of a teacher, and the 

 self-taught student ■ can only expect to master parts 

 of it. But to master any part of it is a training in 

 accuracy which will be useful afterwards, for it will 

 teach the student to leave no part of any specimen 

 unexamined or unexplained. 



A very necessary supplement to the book just 

 named, will be found in T. Jefifery Parker's Lessons in 

 Elementary Biology. This is a book modelled some- 

 what on the general plan of the older volume ; but the 

 plants and animals described in it are more numerous, 

 and for the most part not the same. The arrangement 

 of the book is so complete, and its explanations of 

 the theoretical part of biological study so lucid, that 

 the student cannot possibly do without it, especially 

 as it has the merit of being illustrated, so that it 

 does not, like the other volume, require an atlas to 

 explain it. The principle on which the teaching of 

 both these volumes is based, is expressed in the 

 maxim which has been already quoted in the chapter 

 on classification, that " Natural groups are best de- 

 scribed, not by any definition which marks their 

 boundaries, but by a type which possesses in a 

 marked degree all the leading characters of the 

 class." The elementary student is made thoroughly 

 acquainted with the character of certain typical 

 organisms, before being introduced to the names and 

 definitions of classes — a mode of teaching by which 



