PREFACE TO THE FOURTH EDITION. 



AYiTH regard to the present Edition of this work, the Author 

 has only to say that he has submitted it to a thorough revision, 

 and, to the best of his ability, has brought it up to the present 

 standard of our knowledge. As the work is strictly elemen- 

 tary, and is intended solely for the use of Junior Students, it 

 has not been deemed advisable to make fundamental altera- 

 tions in its general plan, or to materially change the classifi- 

 cation followed in previous Editions, save in those instances 

 in which there is now a general consensus of opinion. The 

 more important recent additions to our acquaintance with the 

 existing or extinct fauna of the world have, however, been 

 noticed in the text, and fresh illustrations have been introduced 

 where this appeared to be desirable. 



University, Aberdeen, 

 December 1885. 



