HOW ANIMALS DEVELOP 



I have put forward are those most generally held 

 by people who are working at embryology at the 

 present day, but to-morrow we may discover some 

 new fact which will force us to modify them. When 

 one is brought face to face with the most fundamental 

 questions about living things, one cannot expect to 

 obtain complete answers in the comparatively short 

 time during which biology has been actively studied. 



C. H. W. 



CAMBRIDGE 

 1935 



ACKNOWLEDGMENTS 



For permission to reproduce illustrations acknow- 

 ledgment is made to the Cambridge University Press 

 (Engelbach, Endocrinology ; Behrens and Barr, Endo- 

 crinology; Huxley and de Beer, Experimental Embryo- 

 logy), Messrs. Longmans, Green & Co. (Quain, 

 Anatomy), Messrs. Macmillan & Co. (MacBride, 

 Invertebrate Embryology), the Railway Gazette (photo- 

 graph of Whitemoor Marshalling Yard, L.N.E.R..), 

 and to my own publishers (Durken, Experimental 

 Analysis of Development; Stockard, Physical Basis of 

 Personality) . 



