STUDIES ON GEKM CELLS 439 



When various stains were used it was found that the Ectoso- 

 men became colored much Hke the cytoplasm. For example, 

 when stained in methylen blue followed by eosin, the chromo- 

 somes were blue and the Ectosomen and cytoplasm red, and when 

 stained by the methy Igreen-fuchsin-orange G method of Hei- 

 denhain the chromosomes were green and the cytoplasm and 

 Ectosomen red. 



Amma also attempts to explain the fact that the Ectosomen 

 appear at only one end of the first cleavage spindle and in only 

 one of the cleavage cells until the two primordial germ cells are 

 formed. He rejects Haecker's hypothesis that the centrosomes 

 possess an unequal influence upon the Ectosomen and that one 

 centrosome attracts all of them because it is stronger than the 

 other, and is inclined to favor the idea that the Ectosomen are 

 the visible evidence of an organ-forming substance which is thus 

 distinguished from the rest of the cytoplasm as 'Kornchenplasma.' 

 Amma's statement is, "dass im Zellplasma des noch ungefurchten 

 Copepodeneies ein vom ubrigen Eiplasma qualitativ verschiedenes 

 Kornchenplasma ezistiert, welches die organbildende Substanz, die 

 Anlagesubstanz fiir die Geschlechtsorgane darstallt" (p. 564). 



Kiihn ('13) has studied the Keimbahn in the summer egg of a 

 Cladoceran, Polyphemus pediculus, and has confirmed certain 

 parts and corrected other portions of the work done by earlier 

 investigators — Grobben ('79), Samassa ('93), and Weismann and 

 Ischikawa ('89). In this species usually one (but sometimes two 

 or three) of the nurse cells (fig. 18, A) passes into the egg before 

 cleavage. This cell (or cells) becomes imbedded near the 

 periphery at the vegetative pole (fig. 18, B, n). During each 

 of the early cleavage divisions this nurse cell is confined to one 

 cell (fig. 18, C-E) which gives rise during the third cleavage (8 to 

 16-cell stage) to the primordial germ cell, containing the remains 

 of the nurse cell (fig. 18 E, K) and to the primordial entoderm 

 cell which does not receive any part of the nurse cell (fig. 18, E, e) . 

 The primordial germ cell and primordial entoderm cell do not 

 divide as quickly as the other blastomeres during the succeeding 

 cleavage stages, a fact that aids in their identification. While 

 the egg is undergoing cleavage, the nurse cell is gradually chang- 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 3- 



