vi PREFACE 



those least deviating from the hypothetical type, as for example, in the 

 order: locust, dragonfly, honeybee, blowfly, Isotoma, polyembryonic 

 Hymenoptera. From time to time a comparative study is made of the 

 different types, and controversial topics are discussed. 



For the benefit of the research student, reference lists are given at the 

 end of each chapter. No pretense is made as to their completeness, 

 especially those in Part I, but it is hoped that they are sufficiently com- 

 prehensive to prove useful to investigators. 



The bibliography, though extensive, is restricted chiefly to books and 

 papers dealing with embryology proper. References to borderline sub- 

 jects such as the physiology and cytology of the embryo and postembry- 

 ology are included only when referred to in the text. Reviews on the 

 subject of physiology and biochemistry and references relating to them 

 may be found in the texts of Needham (1931) and Wigglesworth (1939). 

 Only the briefest outline is given of spermatogenesis and oogenesis. 

 These subjects are fully treated in the texts on cytology by Agar, Don- 

 caster, Schroeder (Depdolla), Sharp, and Wilson. Because of the 

 increasing attention paid to experimental embryology a chapter is 

 devoted to it. This chapter is largely an abstract of an article by 

 Richards and Miller, to whom credit is due. 



The authors have been fortunate in having had at their disposal 

 embryological material of representatives of the major orders, prepared 

 in part by themselves and in part by colleagues and advanced students. 

 Figures taken from the works of others have all been redrawn and in 

 many cases conventionalized. Those not acknowledged in the legends 

 are from the following sources: Butt, Figs. 234-242, 246, 255, 258, 313- 

 326; Escherich, 329, 330, 331B, 333-336; Fernando, 167-174; Heymons, 

 109-112; Johannsen, 295-312; Knower, 133-135; Leiby and Hill, 259-264; 

 Muir and Kershaw, 197-201; Noack, 327, 328, 331^, 332; Noskiewicz 

 and Poluszynski, 217-233; Patten, 286-294; Patterson, 265-275; Phil- 

 iptschenko, 63-99; Roonwal, 137-166; Scholzel, 175-180; Seidel, 202, 

 203, 207, 209-211; Strindberg, 215, 216; Toth, 182-187; Uzel, 100-108; 

 Webster and Phillips, 190-196. Figures in Part I not otherwise acknowl- 

 edged are copies of diagrams used in the authors' classes. Permission 

 to use Figs. 128B-132 from an unpublished paper was given by its author 

 Dr. L. C. Pettit. Figures published for the first time and drawn by the 

 junior author from his own preparations are the following: 113-116, 

 119-126, 204-206, 208, 212, 243-245, 247-254, 256, 257, 276-280, 284, 

 285. To the publishers, the Schweizerbart'sche Verlagsbuchhandlung 

 of Stuttgart, we are indebted for permission to use Figs. 337-361 from the 

 work of Prof. Heymons on Scolopendra, and to Dr. R. Wiesmann for 

 permission to use Figs. ISQA-E from the text of Leuzinger, Wiesmann, 

 and Lehmann. 



