STUDIES ON GERM CELLS 



I. THE HISTORY OF THE GERM CELLS IN INSECTS WITH SPECIAL 

 REFERENCE TO THE KEIMBAHN-DETERMINANTS. » 



II. THE ORIGIN AND SIGNIFICANCE OF THE KEIMBAHN-DETER- 

 MINANTS IN ANIMALS. 



ROBERT W. HEGNER 



From the Zoological Laboratory of the University of Michigan, Ann Arbor, 



Michigan, U.S.A.^ 



SEVENTY-FOUR FIGURES 



CONTENTS 



General introduction 376 



I. The history of the germ cells in insects with special reference to the Keim- 



bahn-determinants 379 



1. Introduction 379 



2. Diptera 380 



A. Historical account 380 



B. The Keimbahn in Miastor americana Felt " 387 



C. The Keimbahn in Compsilura concinnata Meig 398 



3. Coleoptera 4C0 



A. Historical account 400 



B. Nuclear division and differentiation in the eggs of Chrysomelid 



beetles 408 



C. The growth of the oocytes and development of testicular cysts 



in Chrysomelid beetles 413 



(1) The differentiation of nurse cells and oocytes in the ovary 



of Leptinotarsa decemlineata 414 



(2) The origin of the pole-disc granules in Leptinotarsa decem- 



lineata 417 



(3) The spermatogonial divisions and formation of cysts in the 



testes of Leptinotarsa decemlineata 420 



(4) Amitosis in the germ cells of Leptinotarsa 424 



4. Hymenoptera 428 



' Contributions from the Zoological Laboratory of the University of Michigan, 

 and the Marine Biological Laboratory, Woods Hole, Mass. 



375 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 3 

 SEPTE.MBER, 1914 



