192 The Structure of Protoplasm 



tional stretching of its materials." The continued contraction of the 

 band produces the secondary furrow. "The pigmented cortex bound- 

 ing the hghtly pigmented 'primary furrow' becomes the site of 

 intense growth directed toward the egg interior." There is no 

 growth. The continued contraction of the band deepens the furrow 

 and pulls on the cortex adjoining the 'primary furrow', indicating 

 that the cortical layer is in the gel and not in the fluid state. "Vitally- 

 stained marks placed in this position are drawn out into long delicate 

 hair-lines as the furrow deepens." This is just what one would 

 expect if the cortex is stretched or pulled down into the furrow. 



"The streaming of the peripheral cytoplasm from the sides of the 

 egg into the furrow, which has been described by a number of 

 persons, is noticeably absent in the cortex. The streaming observed 

 was in all probability a subcortical movement only, as has been 

 suggested by Motomura also. This is supported by the recent work 

 of Motomura, and of Brown, as well as of my own work, which shows 

 that the cortex (of the Strongylocentrotus, Arbacia, and Triturus 

 eggs, respectively) is a more or less rigid layer during cell division." 

 I suspect that the "streaming of the peripheral cytoplasm" was 

 invented to explain how the pigment granules moved toward the 

 equator and down into the walls of the furrow. This flow, or surface 

 current, as it has frequently been called, seemed to demand that the 

 cortex change from the gel to the liquid state. Thus error leads to 

 error. This flow, as already noted, is not a flow, but is a stretching 

 and pulling down of the gel layer into the furrow. 



"A reasonable explanation of the observed cortical growth, in 

 view of its localized character, is that the increase may be due to an 

 inhibition process, which of course, does not imply that the cortex 

 becomes 'fluid'. Indeed, there are indications that the cortex of the 

 furrow, excepting a small part near its tip, does not differ much in 

 viscosity from the rest of the egg cortex. At least, the difference is 

 not great enough to give rise to the characteristic surface contours 

 of fluids in contact with relatively solid materials. It is well known 

 that the swelling pressure of bio-colloids may attain high values 

 under proper conditions, and the relatively fluid material which 

 Chambers ascertained in the equatorial region of the cleaving eggs 

 would offer little resistance. It is also possible that the growth of 

 the furrow cortex is by intersusception of clear cytoplasm of sub- 

 cortical origin; this might explain the part played by the cytoplasm 

 which some workers have seen streaming toward the furrow. Both 

 processes might be involved, since they are obviously not antago- 



