194 PROBLEMS OF FERTILIZATION 



segmented, and many lived until the third day and 

 formed a rudimentary skeleton, but then died. The 

 characters developed were exclusively maternal. The 

 sperm of certain other starfishes was less effective, but 

 that of. a brittle star was equal to Asterias. Only those 

 eggs developed into which a spermatozoon penetrated, 

 but some eggs which formed membranes failed to seg- 

 ment, and Loeb and his students showed that in these 

 cases the membrane had been caused by external action 

 of the spermatozoon alone. Loeb could not succeed 

 in fertilizing the eggs of Arbacia with the sperm of 

 Asterias by this method. 



The starfish sperm affect the sea urchin egg only in 

 the presence of the alkali; eggs or sperm previously 

 treated with alkali will not react when brought together 

 in pure sea -water. The effect may be on the spermato- 

 zoon or on the egg or on both; but it is obvious that 

 some surface reaction of the egg and spermatozoon is 

 favored by the alkali, because when the sperm once 

 gains entrance to the egg it calls forth the further 

 necessary reactions within it. 



In attempting a further analysis of this subject 

 Loeb (1914) discovered that if the sea urchin eggs are 

 deprived of their jelly by action of HC1 they cannot 

 be fertilized by starfish spermatozoa with the same use 

 of hyperalkaline sea-water that readily brings about 

 fertilization in the presence of the jelly, although they 

 are readily fertilized with their own sperm. But if an 

 excess of calcium is added to the hyperalkaline sea- 

 water the heterogeneous fertilization succeeds in the 

 absence of the jelly, and in this case practically all of 

 the eggs that form membranes segment. In the pres- 



