74 Specificity in Fertilization 



this the writer concluded that the fertilizing power 

 depends on a rapidly reversible action of the alkali on 

 the surface of the two gametes. It was found that 

 an increase of the concentration of calcium in the sea 

 water also favoured the entrance of the Asterias sperm 

 into the egg of purpuratus; and that if CCa was in- 

 creased it was not necessary to add as much NaOH. 



The spermatozoon enters the egg through the so- 

 called fertilization cone, i. e., a protoplasmic process 

 comparable to the pseudopodium of an amoeboid cell. 

 The analogy of the process of phagocytosis — i. e., the 

 taking up of particles by an amoeboid cell — and that of 

 the engulfing of the spermatozoon by the egg presents 

 itself. We do not know definitely the nature of the 

 forces which act in the case of phagocytosis — although 

 surface tension forces and agglutination have been 

 suggested ; both are surface phenomena and are rapidly 

 reversible. 



We should then say that the specificity in the process 

 of fertilization consists in a peculiarity of the surface 

 of the egg and spermatozoon which in the case of S. 

 purpuratus 9 and Asterias & can be supplied by a 

 slight increase in the COH or CCa. 



By this method fifty per cent, or more of the eggs of 

 purpuratus could be fertilized with the sperm of the 

 starfish Asterias ochracea, capitata, Ophiurians, and 

 Holothurians, while with the sperm of another starfish, 

 Pycnopodia spuria, only five per cent., and with the 



