INTRODUCTION. 



nnHIS book is a handbook, not a text-book, and the 

 entire absence of generalization and comparison is 

 not due to indifference to the generalizations of modern 

 philosophical morphology, but rather to a wish to aid 

 beginners to study them. 



Most lecturers upon natural science find, no doubt, 

 that preliminary work, the presentation of the facts upon 

 which science is based, absorbs so much time that there 

 is no room for a philosophical discussion of the scien- 

 tific aspects of the subject. 



I have, therefore, attempted to show the student how 

 to acquire a knowledge of the facts for himself, in order 

 to remove this burden from lecturers and text-books. 



The types selected for description are necessarily few ; 

 but I hope that a thorough study of all the forms which 

 are here described will fit the student for more exten- 

 sive research. 



In the treatment of each type I have not attempted 

 to make an exhaustive monograph for the use of special- 

 ists, or to present all that is known about it ; but sim- 

 ply to call the attention of the beginner to the struc- 

 tural features which he can readily observe for himself. 



