PREFACE. 



So many books have recently come out, and are still 

 coming out, on zoology and biology that it seems neces- 

 sary that I should say something of the reasons for 

 this one. 



Nearly all the books now coming out are devoted, 

 and rightly so, to practical laboratory methods, and 

 especially to the study of selected types. This method, 

 first introduced by Rolleston and rendered popular by 

 Huxley, was a reaction against the barrenness of the old 

 text-book and lecture method. It was certainly timely 

 and necessary ; but there is danger that, like all reac- 

 tions, it may have, and indeed has already, gone too far. 

 Undoubtedly the teaching by types is indispensable in 

 the early part of the course, in order to introduce the 

 student into the true spirit and methods of science ; but 

 to continue it and "make it the main form of teaching 

 is a serious mistake." * There is serious danger that in 

 the attempt to explore thoroughly a few small spots 

 here and there in the field we lose sight of the general 

 connection of all parts to one another and to the whole 

 — that in the microscopic clearness but narrowness of 

 our knowledge we lose that general view of the whole 

 which alone gives significance to any knowledge. 



Such a general view of the physiology and morphol- 

 ogy of the animal kingdom is, it seems to me, a great 



* Lankester, Nature, Iviii, 25, 1898. 



