iv Preface. 



ject is being used as an introductory one. In many respects the con- 

 tinuous study of a single animal is a good corrective for the rough 

 general kind of dissection as suggested by the zoological textbooks, and 

 may be made to share the well-known merit of human anatomy as a 

 laboratory discipline. Again, for the student who afterwards is con- 

 cerned with vertebrate evolution, the study of a specialized type, such 

 as a mammal, gives him, at the outset, something definite and concrete 

 on which to base his conceptions of sequence. Primitive structure is of 

 great value as a means of explanation, but the question, now as hereto- 

 fore, is whether or not the study of primitive animals as a preliminary 

 step represents the correct procedure from a laboratory standpoint. 

 The more the student becomes interested in tracing sequence, the more 

 he will be convinced of the necessity of stating his problem before he 

 begins to solve it. 



The practical outlines on which the present book is based have been 

 used for several years and in different forms in the laboratories of the 

 University of Toronto. It would be difficult to make due acknowledg- 

 ments to those colleagues and students who at one time or another have 

 assisted in its preparation. Indeed, our chief obligation is to Professor 

 Ramsay Wright, who, in establishing laboratory courses of this kind, 

 has laid the foundation on which we have tried to build. 



B, A. BENSLEY. 

 University of Toronto, 



January 3rd, 1910. 



