226 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



fluids mixed with the sperm. Control experiments, however, 

 showed that this was not the case with the eggs of S. purpuratus. 



In one experiment, all the eggs of a female purpuratus formed 

 membranes when placed in a mixture of 50 c.c. of sea-water + 

 O.Gc.c. N/10 NaOH, to which was added only a few drops 

 of living Asterias sperm. However, only a few of these eggs 

 (only a fraction of 1 per cent) developed to larvae; the others 

 disintegrated in the manner characteristic of eggs which have 

 not been treated with a hypertonic solution subsequently to 

 artificial membrane formation. This membrane formation, 

 however, was brought about in this case through the living 

 spermatozoa and not by the body fluids of the starfish; this 

 point, which is important, was established by adding to the 

 same eggs sperm from the same Asterias male after heating it 

 to 50, in which case no egg formed a membrane. Even on 

 addition of ten times the amount of (dead) sperm which was 

 sufficient in the living condition to cause all the eggs to form 

 membranes, membranes were formed by only a few of the 

 eggs, even after a duration of several hours and when the eggs 

 were thoroughly shaken and mixed with the sperm. Hence 

 the membranes in the above-mentioned experiments were 

 formed by the living spermatozoa and not by any admixture 

 with the sperm. 



While all the eggs of S. purpuratus form membranes under 

 the influence of living sperm within an hour, only a fraction of 

 the eggs (which varies in different cases) develops into larvae. 

 The rest of the eggs behave as if the sperm had only brought 

 about the artificial membrane formation by the giving-off to 

 the eggs of a substance which acts like butyric acid. The 

 explanation of this result is probably as follows. The sperm of 

 the starfish penetrates only slowly into the sea-urchin egg; the 

 starfish spermatozoon lingers for a long time in contact with 

 the protoplasm of the sea-urchin egg before it gets into the in- 

 terior. The time during which the spermatozoon lingers in 



