GERM CELLS IN THE ARTHROPODA 111 



Hegner (1908, 1909a, 19096, 1911a, 19116, 1914a), 

 and Wieman (1910a, 19106) will be referred to in 

 the following paragraphs. 



Wheeler (1889) figured several primordial germ 

 cells in an egg of Leptinotarsa with a segmented germ 

 band and suspected 

 their true nature, but 

 did not discover them 

 in earlier stages. Le- 

 caillon (1898) de- 

 scribed the pole-cells 

 in several chrysomelid 

 beetles, but did not 

 make out any of the 

 details concerning 

 their origin, structure, 

 and migrations. 



Within the last 

 seven years the writer 

 has devoted a consid- 

 erable portion of his 

 time to morphological 

 and experimental 

 studies of the eggs of 

 beetles, particularly 

 Calligrapha bigsbyana, C. multipunctata, C. lunata, 

 and Leptinotarsa decemlineata. The eggs of these 

 species are peculiarly favorable for study, since they 

 are definitely oriented in the body of the mother 

 and various surfaces can be recognized in the newly 

 laid egg : they can be placed under the most severe 



FIG. 34. Calliphora. A. Longitudi- 

 nal section through posterior end of 

 freshly laid egg, showing " Dotter- 

 platte (Dpt). B. Longitudinal sec- 

 tion through posterior end of egg at 

 time of blastoderm formation, showing 

 protrusion of primordial germ cells 

 (p.g.c.). (From Noack, 1901.) 



