vi PREFACE TO THE THIRD EDITION. 



which they have done their work. I am also indebted 

 to Dr. Traquair for allowing me to figure some of the 

 specimens in the Edinburgh Museum of Science and 

 Art. In regard to the illustrations, I may further say 

 that in almost every case they have either been derived 

 from original memoirs and works of reference, or drawn 

 from specimens. Of course, no one who has worked 

 with such excellent practical books as that by Marshall 

 and Hurst or Parker's Zootomy, can help being assisted 

 by them in preparing analogous diagrams ; but I have 

 refrained from incurring any but an absolutely necessary 

 debt. 



J. A. T. 



The University, 



Aberdeen, April 1899. 



