SUSCEPTIBILITY OF EGGS TO CYANIDE. 139 



fertilization. There then ensues a period of retrogression of the 

 aster, the astral radiations fade out, and the nucleus grows enor- 

 mously. This is the immune period. At the end of that time 

 the nuclear membrane disappears very rapidly and a great growth 

 of the aster takes place, leading up to the first division. This is 

 the second susceptible period. Following segmentation, the nu- 

 cleus reforms. The asters again decrease in size, and a second 

 period of resistance occurs. This is, however, short, as the second 

 division comes very quickly. 



I have attempted to confirm these observations by studying the 

 living Asterias egg. I got a very fine lot of Asterias eggs, nearly 

 the whole starting maturating within five minutes after shedding. 

 They were fertilized very soon after the germinal vesicle had 

 begun to disappear and transferred at ten-minute intervals (at 

 five-minute intervals during the extrusion of the polar globules 

 and segmentation) to w/ioo, ;//'5O and ;/z/25 sodium cyanide so- 

 lutions. After remaining in the cyanide solution for periods of 

 one, two and three hours they were transferred to fresh sea- 

 water, which was repeatedly changed, and were then left to de- 

 velop. 



The results were very unsatisfactory. No sharp periods of 

 susceptibility could be discovered in which the majority of the 

 eggs were killed in the two-cell stage as in Arbacia. This 

 failure could not be attributed, I think, to lack of uniformity in 

 the development of the egg, since they segmented with marked 

 uniformity. In practically all cases development proceeded 

 after removal of the cyanide, although there were in some cases 

 marked differences in the appearance of the embryos in lots in- 

 troduced into the cyanide at different times. Those eggs put in 

 the cyanide immediately after segmentation formed swimming 

 gastrulae which were fairly normal. Eggs introduced into the 

 cyanide immediately before segmentation had the larger number 

 of dwarf and irregular blastulse and disintegrating eggs. Fre- 

 quently the eggs after removal from the cyanide did not segment 

 for several hours and then broke at once into a mass of spheres, 

 some of which died, while others formed the embryo. 



The resistance of the eggs was remarkable. One series was 

 left for three hours in w/25 cyanide, and the great majority of the 



