THE ORIGIX AXD EARLY HISTORY OF THE GERM- 

 CELLS IN SOME CHRYSOMELID BEETLES. 



BY 



ROBERT WILHELM HEGNER. 



With 4 Plates. 

 CONTENTS 



PAGE 



I. Introduction 231 



II. Review of tlie Literature upon the Origin of the Germ-cells in 



the Insecta 2.32 



Introduction 232 



1. Lepidoptera 2.33 



2. Diptera 230 



3. Heniiptera 243 



4. Hynienoptera 24.5 



5. Orthop.era 248 



G. Coleopt^ra 2.51 



7. Neuroptera 2.54 



8. Dermaptera 255 



0. Aptera 2.55 



III. Observations 2.57 



1. The role-Disc 2.57 



2. The Genesis of the Pole-Cells 258 



3. The History of the Pole-Cells until the Sex of the Em- 



bryo can be Recognized 205 



IV. General Considerations 270 



1. The Granules of the Pole-Disc 270 



2. The Migration of tlie Primitive Germ-Cells in the Insecta. . 270 



A. The INIigration of the Pole-Cells through the Pole- 



Cells Canal 270 



B. Vhe Migration of the Germ-Cells within the Embryo 278 



C. The Method of Locomotion of the Germ-Cells ". . 280 



.3. The Origin and Early History of the Germ-Cells in the 



Insecta 283 



V. Summary 288 



VI. Material and Methods 290 



VI I. Literature List 291 



VIII. Explanatli.n of Plates 290 



I. Introduction. 

 The £rerni-eells of the ]\Ietozoa have been in recent years a favorite 

 subject for investigators. The theory of the continuity of the germ- 

 plasm expressed by Galton in 1872 and Later (1885) elaborated 



The .TotiiXAr. of Morpholooy. — Vol. XX, No. 2. 



