vi Preface 



As years passed, the annual enrollment in the course increased to a 

 maximum of 10 times that of the first few years. Lectures were given in 

 a hall remote from the laboratories. Students could obtain books only 

 by going to libraries more or less distant from the laboratories, and 

 other changes, of intangible nature, occurred. In earlier years the 

 laboratory work was announced as requiring at least six hours a week, 

 and it was generally understood that it might consume indefinitely more 

 according to the interest and efficiency of the individual student. In 

 later years the laboratory work was necessarily restricted to six hours 

 a week and there was little opportunity for work outside the assigned 

 hours. An earlier sense of freedom and leisure to work thoughtfully 

 was insidiously superseded by a sense of crowding, pressure, and haste. 

 As numbers increased, the conducting of the course inevitably became 

 more formal and mechanized So much "ground"' to be "covered," so 

 many facts to be "learned" — scant time was left for thinking. It was 

 the same everywhere — more students, relatively fewer teachers, 

 schools forced to adopt factory methods calculated to achieve "mass 

 production." 



The point at which the foregoing historical sketch is aimed is that 

 the indication of appropriate "collateral reading" became increasingly 

 a problem. It was evident that the student of the later years was not 

 reading much and could not be expected to. It was therefore important 

 to recommend a few books so selected as to cover the general field as 

 broadly as possible. This necessity led to the search for those few books 

 which, collectively, would enable the student to obtain a reasonably 

 adequate knowledge and appreciation of the field. The search for these 

 books tended to emphasize the shortcomings (for the purpose in hand ) 

 of the individual book. There were, and are, books which give excellent 

 descriptions of structure but with little or no reference to function; 

 books which adequately cover comparative anatomy but with quite 

 inadequate treatment of classification — i.e., books which compare 

 organs but do not compare animals; books which describe types (a 

 representative animal of each large group) but do not bring the cor- 

 responding structures of the several types into close comparison ; books 

 which talk about homologous organs but do not give the reader any 

 information as to what homology is and what significance it has; few 

 books on comparative anatomy which offer even a brief survey of the 

 history of chordates. 



In any treatment of comparative anatomy there are two especially 

 puzzling problems. One is presented by the necessity of giving some 

 account of embryonic development. It is difficult to give a clear descrip- 

 tion of the embryonic stages of an organ to a reader who has little or no 

 knowledge of the nature and structure of the organ in the adult. But 



