CELL DIVISION — SPINDLE IN SEA-URCHIN EGGS 231 



In order to determine the concentration of KCN necessary to 

 suppress division, I made a 0.004 per cent solution^ in sea-water 

 by diluting a 1 per cent solution (in distilled water) with 249 

 parts of sea-water. This 0.004 per cent solution was successively 

 diluted with equal parts of sea-water until nine solutions were 

 obtained, each half the concentration of the preceding one. 

 Eggs were subjected to all these solutions, and it was found that 

 a concentration of 0.000625 per cent sufficed to check segmenta- 

 tion. In concentrations of 0.0000313 per cent and 0.0000156 

 per cent, segmentation proceeded to about the four-cell stage, 

 but then went no further. 



The following experiment shows that the early stages of mito- 

 sis can occur in concentrations much above those which inhibit 

 the entire process: 



June 25th. Eggs were fertilized at 5:18| p.m. In these eggs the 

 spindle first began to be visible twenty minutes later (at 5:39 to 5:40 

 P.M.). At 5:23 P.M., 5:27 p.m., 5:32 p.m., 5:38 p.m., some of the fer- 

 tilized eggs were transferred into Stender dishes A, B, C, D, respec- 

 tively. Each of these dishes contained 0.0025 per cent KCN, prepared 

 by diluting 1 per cent KCN (in distilled water) with 399 parts of sea- 

 water. 



The €ggs in A were observed at 5:47 p.m. Instead of showing a 

 small nucleus, they showed a large pale spot with a vague border. 

 This spot was often elongated, and probably represented an abnormal 

 spindle. When the eggs in B were examined at 5:58 p.m., they showed 

 a pre-spindle plainly, and they appeared much like the normal eggs. 

 None of the eggs in A, B, C, D, proceeded to develop any further than 

 the spindle stage, and observation at 10:40 p.m. showed them all with 

 spindles, but unsegmented. 



It might be thought that the above experiment owes its ex- 

 planation to the fact that the cyanide penetrates the eggs slowly, 

 and that only after a time is its influence felt. However the eggs 

 in D appeared to be checked almost immediately. Moreover, a 

 later experiment showed that this interpretation could not be the 

 correct one. In this case the fertilized eggs were put into a 0.004 

 per cent solution of KCN in sea-water five minutes after fer- 

 tilization. The eggs in the KCN solution were kept in a test- 



2 Of course the actual concentration of KCN is not referred to, as there is a 

 reaction between KCN and the salts of sea-water. 



