160 GERM-CELL CYCLE IN ANIMALS 



without the disintegration of the migrating chroma- 

 tin. In plants also Gates (1911) has shown that 

 chromatin may migrate from one pollen mother-cell 

 of (Enothera gigas into a neighboring mother-cell 

 where it remains visible for some time before be- 

 coming incorporated with the surrounding cyto- 

 plasm. Many more cases of cellular fusion might be 

 mentioned, but in no instance so far as I am aware 

 has the union of two well-developed oocytes to form 

 one egg been reported. It is true that in Copido- 

 soma the chromatin in one (the proximal) oocyte 

 (the keimbahn-chromatin) finally disintegrates and 

 disappears in the cytoplasm, and thus the condition 

 here may be compared with that in the cases men- 

 tioned above, but the stage of fusion in Copidosoma 

 is extremely late in the growth period, and the 

 chromatin material remains visible for a remarkably 

 long interval of the germ-cell cycle. 



According to Silvestri the first cleavage cell of 

 Copidosoma consists of the egg nucleus surrounded 

 by only a small portion of the substance in the pos- 

 terior end of the egg in which is embedded the keim- 

 bahn-chromatin. If the two materials within the 

 oocytes do not become intimately fused, it is obvious 

 therefore that the cells of the embryo which are 

 descended from the first cleavage cell are derived 

 from the nucleus of the anterior of the two fused 

 oocytes and cytoplasm from the posterior oocyte 

 with the addition of the keimbahn-chromatin. 



The history of the germ cells after their segrega- 

 tion is not known for any polyembryonic animal. 



