Germ-Cells in Clirysoinelid Beetles. 239 



Weismann described in one egg of Chironomus sp. a nucleated 

 protrusion at the anterior end Avliicli was capable of amoeboid move- 

 ments and probably migrated upon the surface and was lost to 

 view. In another case no nucleus was visible, but the anterior ball 

 of protoplasm divided into eight bodies of different sizes, which after 

 fifteen minutes dissolved. These were thought to be polar bodies, 

 but might easily have been mistaken for pole-cells. 



The pole-cells were accurately traced to the definitive germ-glands 

 by Balbiani (1882, 1885) in Chivonoinns. One pole-cell usually 

 appeared first; but, as previously observed by Grimm (1870) and 

 Weismann (1882), sometimes two were protruded simultaneously. 

 These two divided to form four and then eight pole-cells. Snmll 

 non-nucleated protoplasmic globules were pushed ont of the egg at 

 both anterior and posterior ends, disintegrating later into a mass of 

 granules in the polar cavities. Balbiani claimed that Robin (1862) 

 and Weismann (1863), both of whom recorded twelve or more pole- 

 cells, were deceived by these globules, as there should have been only 

 eight pole-cells. These droplets would also explain the protrusion 

 discovered by Weismann (1882) at the anterior end of the egg. 

 Balbiani, however, did not find the anterior nucle:ited globides which 

 Weismann considered polar bodies. He agreed with previous workers 

 that the pole-cells did not arise by free formatiou during or after 

 germination (Robin, 1862, Weismann, 1863), l)ut were derivatives 

 of the cleavage nucleus (Leuckart, 1865, Metschnikoff, 1866, Grimm, 

 1870). After the first division of the segmentation nucleus the 

 anterior daughter nucleus ])rol)ably gave rise to the blastodermic 

 nuclei of that region, while the posterior furnished the two pole-cell 

 nuclei and those of the posterior blastoderm-cells. After the eight 

 pole-cells were formed, an elongation of the vitcllus forced the group 

 against the egg membrane causing a blastodermic depression. 



In the next stage the pole-cells were found inside of the blasto- 

 derm, but Balbiani did not determine whether they passed through 

 it, or a clear space was left in the blastoderm for their entrance. 

 They now consisted of two separate nmssc'^, each containing two 

 quadrinucleatcd cells. This wa< su]iposed to have come about in the 

 following manner. The eight original pole-cells fused in pairs, 



