Vlll .PREFACE. 



should find himself fully able to comprehend the Introductory 

 portion of the work, whilst still standing at the threshold of 

 the subject. Whilst the student, therefore, will do well to 

 glance over the Introduction before commencing the study 

 of the systematic portion of the work, he must be prepared to 

 find many points which he can only fully grasp after he has 

 attained a knowledge of the leading modifications of structure 

 exhibited in the Animal Kingdom. The Author has only 

 to add that the first part of the work (on the Invertebrate 

 Animals) has been carefully revised, and, as far as possible, 

 brought up to the present level of the Science; whilst the 

 illustrations, with very few exceptions, have been drawn upon 

 the wood by himself. 



EDINBURGH, December i, 1870. 



