382 ROBERT W. HEGNER 



that the first pole-cell appeared 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 granules which, 

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

 nal 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 accord through the blastoderm which closed after them. 

 They now lay at the posterior end of the germ-band from whence 

 they were possibly moved anteriorly by the growing forward of 

 the entomesoderm. The mass of pole-cells finally divided into 

 two groups which 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. 



Ritter was the first to determine the fact that the 'yolk masses' 

 contained in the pole-cells of Chironomus are derived from a 

 definite structure and are not chance acquisitions from the yolk 

 granules in the egg. After giving a brief sketch of the polar 

 bodies. and male and female pronuclei, he says: 



In dem nachsten Stadium sind in dem Dotter keine Zellen mehr zu 

 sehen; dagegen tritt an demjenigen Pol, an welchem spater die Pol- 

 zellen erscheinen, also an dem hinteren, ein eigenthlimlicher wulstartiger 

 Korper auf, welcher durch das Hamatoxylin sehr dunkel gefarbt wird. 

 Er erscheint auf mehreren Schnitten und stellt eine etwas nach oben 

 vorgewolbte Platte dar, welche vielfach runde Fortsatze zeigt und aus 

 feinkornigem Protoplasma besteht. Er l^leibt bis zum Austritt der 

 Polzellen an derselben Stelle. 



Ritter then gives a fragmentary account of the early divisions 

 of the cleavage nucleus, at the end of which, the two first pole- 

 cells appear each containing a ''grossen Kern und um denselben 

 herum kranzformig einen Theil des obengenannten dunklen 

 wulstformigen Korpers." This darkly staining body he called 

 'Keimwulst.' 



That the 'Keimwulst' played an important role in the segrega- 

 tion of the germ cells was quite obvious to Ritter, but he was in 

 «rror when he stated that this body contained the first cleavage 



