CELL DIVISION — SPINDLE IN SEA-URCHIN EGGS 227 



eggs had segmented, some of these had stopped at the two-cell stage, 

 but others had gone on. In h, 98 per cent had segmented, and almost 

 all were normal. In c to g normal segmentation of course occurred. 



At about 7 P.M., a to ^ were examined for blastulae. In a, about 

 2 per cent of the eggs had developed motile blastulae. In b to g, prac- 

 tically all the eggs had developed to motile forms, only immature eggs 

 remaining on the bottom of the dish. The eggs in A to G^ were then 

 examined. No motile blastulae were found in A to E, in F and G, mo- 

 tile blastulae were abundant. 



July 28th. Ethyl nitrate. Eggs were fertilized at 11:50 a.m. and at 

 12 M they were placed in vials A to F. Vial A contained 0.5 per cent 

 ethyl nitrate in sea-water, B 0.4 per cent, C 0.3 per cent, D 0.2 per cent, 

 £'0.1 per cent, and F 0.05 per cent. 



At 12:06| P.M., eggs in C and normal fertilized control eggs were cen- 

 trifuged simultaneously, the handle being turned 50 times in 30 seconds. 

 The eggs in C had a hyaline zone extending through half the egg, in the 

 normal eggs the hyaline zone was not distinct, but was indicated in a 

 fourth of the egg. At 12:19 p.m., eggs in A and normal eggs were cen- 

 trifuged simultaneously, the handle being turned 50 times in 30 seconds. 

 The eggs in A showed a hyaline zone extending halfway. In the nor- 

 mal eggs, the cytoplasmic gelation had reversed, and the hyaline zone 

 extended one-third of the distance along the axis of stratification. 



At 12:30 P.M., some eggs were removed from each of the vials A to F 

 and transferred to normal sea-water in Stender dishes a to /, respec- 

 tively. In 6 to / normal segmentation occurred and motile blastulae 

 were produced. In a, some eggs segmented normally, others abnor- 

 mally; a few motile blastulae resulted. Of the eggs which remained 

 in A to F, those m. A, B, C, did not segment, those in D, E, F, seg- 

 mented abnormally. No blastulae were produced in A to F. 



It is scarcely necessary to mention other experiments of the 

 same sort which were performed with the various substances pre- 

 viously enumerated. All fourteen substances, in suitable con- 

 centration, prevent the appearance of the mitotic figure without 

 otherwise injuring; the egg. Those concentrations which act in 

 this way are the very ones which inhibit gelation and preserve the 

 fluid condition of the cytoplasm. 



Perhaps the action of these substances depends upon their 

 lipoid-solvent action. This action does not appear to be exerted 

 on the plasma-membrane, as many students of anesthesia have 

 thought, for the vitelline membrane, which I have shown ('15) 

 to be the plasma membrane of the unfertilized egg, is, as far as 

 I can determine, morphologically unaffected. Similarly, the 

 hyaline layer, which becomes the plasma membrane soon after 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 30, KO. 2 



