PREFACE 



This text is the outgrowth of a course of lectures on the embryology 

 of insects given by the senior author over a period of twenty years and 

 now being continued by the junior author. It goes without saying that 

 more is offered here than is presented in the time allotted to the subject 

 in Cornell University. From year to year new topics were introduced 

 and old ones laid by so that now from the accumulated subject matter 

 the material for this book has been selected. It may well be, in the 

 opinion of some readers, that certain phases of the subject have been 

 overemphasized and others have not been sufficiently stressed. To this 

 can be said only that an effort has been made to present as balanced a 

 treatment as the available material permits and that research students 

 must of necessity refer to original sources for details that limitation of 

 space prevents being included here. 



The authors have endeavored to preserve an impartial attitude on 

 controversial questions — presenting in Part I the chief views on debat- 

 able points and in the chapters of Part II reflecting the opinions of the 

 several investigators on the subject of their research. Nowhere in the 

 developmental history of the arthropods has the debate been more lively 

 and at times more acrimonious than that relating to the origin of the 

 mid-gut. The student is therefore warned after reading an account 

 of the development of some species in the second part to turn to the first 

 part for a discussion of points of questionable interpretation. 



The subject of embryonic development may be presented in several 

 ways each of which has its advantages and disadvantages. Part I of 

 this text is devoted to a comparative study of the tissues and organs 

 found in the several types of animals considered. In Part II the embry- 

 onic history of a number of insects representing most of the orders is 

 described, emphasis being placed on the more characteristic features 

 of the development of each type. By the selection of illustrative species 

 in the second part which are not especially stressed in the first part, undue 

 repetition is avoided. After some experimenting the authors have 

 adopted in their classes the following method of presentation, it being 

 assumed that the students have had training in elementary insect taxon- 

 omy and anatomy as well as an introductory course in general biology 

 or its equivalent. After a brief introduction and a review of the activi- 

 ties of the animal cell the development of a generalized insect is described 

 in some detail accompanied by charts and blackboard diagrams. This 

 is followed by accounts of the development of a few forms beginning with 



