PREFACE BY PROFESSOR ERNST HAECKEL ix 



wisely chosen and carefully executed illustrations assisting materially 

 in this result. 



It is therefore with great pleasure that I commend this book to 

 the English student, in accordance with the wish expressed by my 

 friend Professor Lang and his translators Mr. and Mrs. Bernard, and 

 in the hope that the English translation will promote to as great an 

 extent as the German original the wider study and better com- 

 prehension of animal morphology, and will attract new students to 

 this noble science. 



ERNST HAECKEL. 



JENA, 1891. 



