PREFACE 



The object of this volume is to sketch in its main outlines the 

 science of Vertebrate Embryology as disclosed by the study of the 

 non-mammalian vertebrates. It is not meant as a work of reference 

 as regards details. The facts of embryology are dealt with as 

 illustrating general principles : large masses of data which have no 

 particular bearing, in the present condition of knowledge, are 

 deliberately omitted. 



It is believed that a volume upon the lines indicated is greatly 

 needed — not merely for students intending to specialize in vertebrate 

 morphology but also for students of medicine who desire to know 

 something of the framework of morphological principles which serves 

 to unite together the detailed facts of anatomy. The science of 

 embryology, in fact the science of animal morphology as a whole, 

 has suffered much through the patient but undiscriminating 

 accumulation of masses of mere descriptive detail which have tended 

 to obscure general principles and incidentally to smother interest in 

 one of the most fascinating of sciences. It is hoped that the student 

 who reads through portions of this book will have at least his 

 suspicions aroused that behind the dull facts of anatomical structure 

 there lies a very charming and living philosophy. 



It has again been one of the misfortunes of vertebrate embryology 

 that its teaching has been dominated in great part by general 

 ideas based upon insufficient data. In an evolutionary science like 

 morphology the real fundamental principles are to be elicited by 

 enquiry into the more archaic types of existing animal life. But 

 the material for the earlier embryological investigations was chosen 

 not for its archaicism but rather for purely practical reasons such as 



