Germ-Cells in Chrysomelid Beetles. 241 



Voeltzkow (1880) stated that in Musca the pole-cells pressed 

 the blastoderm-cells inward forming a wedge which projected into 

 the yolk. Blastoderm-cells separated from this wedge, wandered 

 into the interior, and became the so-called yolk-nuclei. He further 

 stated that "die Polzellen wandern mit dem Keimstrcifen auf die 

 Dorsalseite und in den Enddarm hinein." 



In his work on Calliphora, Graber (1889) described the pole- 

 cells, but not until the blastoderm had formed. They were found 

 outside of the blastoderm-cells and were smaller than the latter, 

 .and stained more intensely. "Ihre Zahl ist eine ziemlich constante 

 und betragi ca 25-35." They were figured in a cross section (Taf. 

 VII, Fig. 91) where they occurred in the amniotic cavity. Graber 

 seldom saw them in Calliphora and never observed them in Lucilia. 



The section method was used by Bitter (1890) in studying the 

 development of the germ-glands in Clii7'onomus. He found that the 

 first pole-cell differentiated at the posterior end of the egg when there 

 were a large number of nuclei scattered about in the yolk. A second 

 pole-cell was protruded close behind the first. Each carried out of the 

 egg part of a flat mass of protoplasmic granules, the "Keimwulst," 

 which, in section, formed a wreath around the nucleus. The two 

 original pole-cells increased by division to four and then to eight. 

 Two divisions of each pole-cell nucleus now occurred, resulting in 

 eight quadrinucleated cells ; these seemed to move of their own ac- 

 cord through the blastoderm which closed after them. They now lay 

 at the posterior end of the germ-band from whence they were pos- 

 sibly moved anteriorly by the growing forward of the entomesoderm. 

 The mass of pole-cells finally divided into two groups w^hich occupied 

 a position on either side of and dorsal to the hind-intestine; there 

 they remained until after the larva hatched, when they became the 

 definitive sex-organs. A more detailed account of Bitter's results 

 will be found in Part IV on the pole-disc. 



The germ-glands were found by Pratt (1893) in Mclopliagus 

 ovinus during the entire larval period. They were small paired 

 structures lying on either side of the abdomen embedded in the 

 fat-body. 



Lowne (1890-95) did not find the pole-cells in the Blow-fly, 



