No. 5S1] ENTRANCE OF THE SPERMATOZOON 



261 



The writer repeated this experiment last winter with 

 the same result. He found that eggs with torn mem- 

 branes when subsequently fertilized with sperm did not 

 form any new membranes as ho had stated before. It is 

 possible that he mistook' at that time the new hyaline 

 membrane which forms around the egg after membrane 

 formation and fertilization for a new fertilization mem- 

 brane. 



It is not necessary that these eggs be fertilized im- 

 mediately after the artificial membrane formation, the ex- 

 periment succeeds also after some time (one hour or 

 more) ; only with this difference that the eggs perish very 

 rapidly after the membrane formation if they receive no 

 second treatment. In order to avoid this difficulty the 

 writer last winter proceeded as follows : Artificial mem- 

 brane formation was produced in the eggs of a purpuratua 

 and all eggs had formed perfect membranes. One con- 

 trol was kept and the rest were shaken. These were di- 

 vided into three lots, one served as a control ; the eggs of 

 the latter all perished as fast as the eggs of the first control 

 (which were not shaken). The second lot were fertilized 

 after about one half hour after membrane formation. 

 Twenty per cent, of these eggs developed into normal 

 larvae, the rest perished. The percentage of developing 

 eggs corresponded roughly with the percentage of eggs 

 whose membrane was torn. The third lot of the shaken 

 eggs was put overnight into 50 c.c. sea water + 7 drops 

 of 1/10 per cent. KCN, to prevent the disintegration of 

 these eggs. The next morning (sixteen hours after the 

 membrane formation) the eggs of Lot 3 were transferred 

 into normal sea water and divided into two lots, one was 

 fertilized with sperm, the other was kept as a control. 

 About twenty per cent, of the eggs which were fertilized 

 began to segment, but many in an abnormal way and 

 none developed into larva?. Of the second lot to which 

 no sperm was added also a few began to segment. As 

 the writer has shown in former experiments, the eggs of 

 Strongyloccntrotus can be caused to develop after artifi- 



