PREFACE TO THE SECOND EDITION 



A NEW edition of this Text-Book has been called for on some- 

 what short notice, and, had it not been for the assistance generously 

 rendered by Professor W. Newton Parker, who has helped me 

 greatly in the revision of the proofs, and has made a large number 

 of useful suggestions, it would have been impossible for me to have 

 completed the work within the time prescribed. Fortunately, also, 

 materials for the most important of the alterations and additions 

 had been already, to a certain extent, prepared. 



The original plan of the work has not been in any way altered, 

 and, though all parts have been subjected to careful revision, there 

 is a good deal, especially in the descriptions of many of the 

 examples, which has not been materially changed. On the other 

 hand, some parts have been to a great extent re-written, and a 

 good many illustrations have been added, a fair proportion of which 

 are new to text-books of this description. 



I have the pleasure of acknowledging assistance on special points 

 received from Professor J. P. Hill, Mr. S. J. Johnston, B.A., B.Sc., 

 Mr. E. J. Goddard, B.A, D.Sc, and Mr. H. L. Kesteven, B.Sc, all 

 of the University of Sydney. A good many of the new illustra- 

 tions were re-drawn by W. Birmingham, Laboratory Assistant, 

 Department of Biology. 



W. A. HAS WELL. 



