AUTHOR'S PREFACE 



There are two methods of teaching Zoology. One method is 

 to deal with a limited number of selected types one by one, 

 and the other is to compare corresponding parts of a number 

 of different animals. Each method has its advantages and 

 its drawbacks. The type method is essential for gaining 

 acquaintance with actual animals, and is of fundamental 

 importance from the fact that it permits of practical study of 

 the complete animals themselves. It cannot be too much 

 emphasised that Zoology is the study of animals, and not the 

 study of books written about them. That being so, it is 

 obviously more convenient to dissect and study one type 

 thoroughly before passing on to the next, than to have a 

 number of dissections of corresponding portions of several 

 animals all going on at the same time. The first two parts of 

 this book are devoted to a study of types carefully selected so 

 as to be of the greatest utility in the interpretation of other 

 forms. Part I deals with the adult structure, and Part II with 

 the modes of development. 



While the type method is necessary for a start, it is attended 

 with certain dangers. Too much attention may be paid to the 

 types themselves and too little to the other animals of which they 

 are but only in a general way typical. There is also the danger 

 that "... a multitude of facts overcrowd the memory if they 

 do not lead us to establish principles. ..." I have sought to 

 remedy this with the help of a comparative treatment of the 

 various organ-systems, which forms the subject of Part III. 

 In this part, the information obtained in Parts I and II is woven 

 into a framework, and other animals of interest are interpolated, 

 so as to present a general view of the organ-systems from the 



