232 Kobert Wilhelm Hemer, 



b'^ 



by Weismann has focused tlife attention of em,bryologists upon the 

 reproductive cells. Many remarkable discoveries have been made 

 in the late stages of the history of these cells, but comparatively 

 little effort has been directed toward their early embryonic develop- 

 ment. The work which forms the basis of the present paper was 

 undertaken in an attempt to clear up some of the problems which 

 have resulted from a large number of disconnected studies on the 

 embryology of the Insecta. The lineage of the germ-cells of Calli- 

 graplia 7nuUijyuncfata is described in the following pages from a 

 preblastodermic stage until the sex of the embryo can be recognized. 

 Two other Chrysomelid beetles, Calligrapha lunata and Leptinotarsa 

 decemlineata, are referred to in the course of the paper, but C. 

 multlpunctata has received the largest share of attention. 



The work was begun at the University of Chicago and was con- 

 tinued at the Marine Biological Laboratory at Woods Holl, Mass., 

 and at the University of Wisconsin. I wish to thank the members 

 of the zoological staffs of these institutions for their kindness and 

 for the facilities granted to me. I am greatly indebted to Professor 

 Wm. S. Marshall for his valuable and generous aid and the use of 

 his extensive library ; and I am also under obligations to Professor 

 C. O. Wliitman for his helpful suggestions and advice. I wish to 

 express my gratitude to my wife for her assistance in cutting sec- 

 tions and in preparing the manuscript for the publishers. 



II. Review of tub Literature upon the Origin of the 

 Germ-Cells in the Insecta. 



Introduction. 



Only a few papers have been devoted exclusively to the origin 

 and early development of the germ-cells of the Insecta. These con- 

 tributions do not represent by any means our knowledge of this 

 subject, for alm,ost every work on general insect embryology con- 

 tains observations on the primitive germ-cells, although usually in 

 a subordinate degree. 



Brandt (1878), Heymons (1891), Graber (1891) and others have 

 ])r()vid('d a more or less complete historical account of this phase 



