vi Preface. 



To reduce my lecture notes to a suitable size, I 

 have had to condense many parts to the smallest 

 bulk, and to leave out many matters of detail, such 

 as many of the recent embryological researches of 

 Lankester, Metschnikoff, Kowalewsky, and others. 



I regret that, owing to the long time that this 

 work (written in 1873) has been going through the 

 press, I have not been able to introduce into it 

 references to recent discoveries, such as that of the 

 unisexuality and tracheal system of Peripatus, &c. 



For the sake of Junior Students, I have printed 

 the chief paragraphs in larger type, the details in 

 smaller, so that the general principles can be more 

 easily grasped. 



I make no claim to originality, but have bor- 

 rowed largely from Gegenbaur, Carus, Haeckel, 

 Huxley, Lankester, Van Beneden, Schmarda, and 

 others. I have endeavoured to avoid the errors of 

 second-hand quotations, and of making extracts from 

 other Manuals, which are easily accessible to Stu- 

 dents; and, having been for fifteen years engaged 

 in the practical study of Comparative Anatomy, I 

 have been enabled to verify very many of the state- 

 ments herein made. 



I return my best thanks to Mr. H. W. Mackintosh 

 for his valuable assistance in correcting the press, 

 and to Professor Reynolds for some suggestions in 

 Chapter I. 



