CELL-DIVISION 



great decrease in width of the hyaline plasma-layer as cleav- 

 age progresses and since by treatment with calcium-free 

 sea-water the presence of the filaments can be demonstrated 

 on eggs throughout cleavage, we reach the conclusion that 

 the egg builds new hyaline plasma-layers constantly. One 

 can not say exactly where in the cytoplasm the hyaline 

 plasma-layer begins, for each filament, the essential struc- 

 ture of the layer, is a granule-free prolongation of the 

 cytoplasm. The activity — amoeboid, spinning, and con- 

 tractile — of the hyaline plasma-layer, so well described by 

 Mrs. Andrews as early as 1897, is due to the behavior of 

 these continuations of the egg-plasma. The filaments of 

 the hyaline plasma-layer are a living part of the living pro- 

 toplasmic system (see also Fig. 36).^ 



As a living and integral part of the tgg, these filaments, 

 we should expect, react as the cytoplasm of which they are 

 continuations. Because of their tenuous and granule-free 

 structure they are physiologically different from the remain- 

 der of the egg. However, any very striking difference in 

 their physical behavior needs to be fully established. It 

 was claimed by Goldschmidt and Popoff- first and later by 

 Gray^ that hypertonic sea-water increases the volume of 

 the hyaline plasma-layer and decreases that of the egg and 

 thus reveals a marked difference between the osmotic 

 properties of the surface-cytoplasm and the remainder of 

 the egg. If this interpretation were correct, I would call 

 this difference in osmotic properties — what Gray calls a 

 fortunate coincidence — a most important discovery. We 

 should use every available fact concerning the behavior of 

 colloids in living protoplasm. Is it true that the hyaline 

 plasma-layer increases in volume whilst the remainder of 



^ Ectoplasviic protrusions on living dividing cells have been early 

 described by ina^iy workers. 



- Goldschmidt and Popoff, igoS. 

 ^ Gray, 1931 . 



279 



