PREFACE TO ‘SECOND EDITION, 
(Ni 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 jhe 
_ loss of any essential, parts. \ 
I have freely availed 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, 
