PREFACE TO FIRST EDITION vii 



out of place in a practical handbook. I also venture to 

 hope that the work may be of some use to students who 

 have studied zoology and botany as separate subjects, as 

 well as to that large class of workers whose services to 

 English science often receive but scant recognition — I mean 

 amateur microscopists. 



As to the general treatment of the subject I have been 

 guided by three principles. Firstly, that the main object of 

 teaching biology as part of a liberal education is to familiarise 

 the student not so much with the facts as with the ideas of 

 science. Secondly, that such ideas are best understood, at 

 least by beginners, when studied in connection with concrete 

 types of animals and plants. And, thirdly, that the types 

 chosen should illustrate without unnecessary complication 

 the particular grade of organisation they are intended to 

 typify, and that exceptional cases are out of place in an 

 elementary course. 



The types have therefore been selected with a view of 

 illustrating all the more important modifications of structure 

 and the chief physiological processes in plants and animals ; 

 and, by the occasional introduction of special lessons on 

 such subjects as biogenesis, evolution, &c., the entire work 

 is so arranged as to give a fairly connected account of the 

 general principles of biology. It is in obedience to the last 

 of the principles just enunciated that I have described so 

 many of the Psotozoa, omitted all but a brief reference to 

 the development of Hydra and to the so-called sexual pro- 

 cess in Penicillium, and described Nitella, instead of Chara, 

 and Polygordius instead of the earthworm. The last-named 

 substitution is of course only made possible by the book 



