PREFACE TO SECOND EDITION. 



IN this Edition it has been made possible to add about 

 50 new Figures as well as a short description of a 

 type of Rotifera. On the other hand, a careful revision 

 of the text and former figures has enabled me to keep the 

 volume to practically the same bulk as before without the 

 loss of any essential parts. 



I have freely ^vailed myself of the numerous criticisms 

 which have been offered, and desire to thank many friends 

 for their valuable aid in this respect, among whom I would 

 specially mention Professor W. C. Mcintosh, Professor 

 Marcus Hartog, Dr H. Gadow, Dr Fraser Harris, Dr 

 E. W. G. Masterman, and Mr F. H. Marshall : to Professor 

 Cossar Ewart I am indebted for permission to reproduce a 

 figure (Fig. 330) from his work on the *' Development of 

 the Horse " : lastly, I have to thank my wife for the pre- 

 paration of a comprehensive Index. 



A word of explanation upon the arrangement of the 

 subject-matter may be found useful. Part I. deals in 

 separate chapters with the general facts and principles of 

 the subject and its relationship to kindred sciences : in 

 Part II. the student is expected to study the types of each 

 group in the museum, or in the laboratory, as the case may 

 be, and then to proceed to the generalisations under each 

 phylum or class. This must ever be the natural way of 

 learning the subject, and has therefore been adopted here. 



ARTHUR T. MASTERMAN. 



New School, School of Medicine, 

 Edinburgh, 



228029 



