PREFACE 



BIOLOGY 



THE publication of this volume has been long delayco^wing 

 to my having been on military duty throughout the year 1900. 

 As in the first volume, I have been guided in my selection of 

 types of animal organisation by the requirements of students 

 reading for the preliminary and intermediate science examina- 

 tions in the Universities of Great Britain. 



A considerable space has been allotted to the leading 

 features of the embryology of the various types, since, as 

 I believe, a just appreciation of the problems of Comparative 

 Anatomy cannot be attained without the study of embryonic 

 as well as adult structures. 



The second volume has been finished under more favourable 

 circumstances than the first, and I hope that it will be found 

 to be free from any serious errors. In the first volume, besides 

 some slips of minor importance, I made a serious error in my 

 description and figure of the truncus arteriosus of the Frog. 

 This was not because, as a friendly critic has suggested, I drew 

 my figure from an abnormal specimen, but because I attempted, 

 when in barracks, to construct my figure and description from 

 the rough drawings of my preparations, and got into confusion 

 in the attempt. A new figure, with the necessary corrections 

 of the text, will be found in the errata attached to this volume. 

 A full and, at last, an intelligible account of the structure of 

 the truncus and the function of the spiral valve is given in 

 the new edition of Ecker & Wiedersheim's " Anatomic des 

 Frosches," by E. Gaupp, 1899, pp. 260 and 283. 



I have to express my obligations to Mr O. H. Latter, M.A., 

 of Charterhouse School, who has kindly read through the 

 proof sheets of this volume and assisted me with many valuable 

 criticisms and suggestions, and to Mr J. W. Jenkinson, M.A., 

 of Exeter College, Oxford, who has helped me in many ways, 

 particularly in placing at my disposal his wide and exact 

 knowledge of the placentation of the Mammalia. 



GILBERT C. BOURNE. 



OXFORD, February 1902. 

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