■viii PREFACE 



single volume, and it was therefore necessary to limit the 

 descriptions mainly to those animals to which the students 

 for whom the book is chiefly intended have to give special 

 attention. This has resulted in rather a heavy balance on 

 the side of Vertebrates ; but on the whole, I think that if 

 sufficient work is done on the lower animals to illustrate 

 certain main facts and generalisations, a comparative study 

 of several Vertebrates forms as good a training as any for 

 beginners — more especially in the case of medical students. 

 I am indebted to Mr. H. Spencer Harrison, B.Sc, 

 Demonstrator of Biology in this College, for much assistance 

 in testing and improving the practical instructions, as well 

 as for various suggestions and for help while the work was 

 passing through the press. The new figures were re-drawn 

 from the originals by Mr. M. P. Parker. 



W. N. PARKER. 



University College, Cardiff, 

 November, 1899. 



