304 THE CELL 



Its hyaline superficial layer raises itself up as a small protuber- 

 ance, thus projecting a receptive prominence (cone d' at traction)- 

 towards the spermatozoon. Sometimes this protuberance is soft, 

 and drawn out in the form of a needle or tongue, and sometimes it 

 is broad and short. After contact with the spermatozoon has 

 taken place, it is withdrawn. 



Fol considers that it is impossible to doubt the accuracy of this 

 observation, and remarks further : " Since we cannot deny the 

 fact that the spermatozoon exercises an influence upon the yolk, 

 from which it is separated by a relatively great distance, we must 

 accept the theory that influence at a distance (action a distance) 

 is a possibility." 



I will confine myself to the above-mentioned observations, the 

 number of which could be easily greatly multiplied, and will only 

 quote the following words of the botanist Sachs (II. 33) : 



" Influence at a distance, or the mutual attraction of sexual cells 

 for one another, is one of the most startling facts connected with 

 the processes of fertilisation. I have chosen this term for the facts 

 about to be more minutely described, as it is not too long, and, at 

 any rate, realistic. We must not, however, take the words, in- 

 fluence at a distance and mutual attraction, exactly in the same 

 sense as in physics. 



" In the numerous desci-iptions which various observers have 

 given of the behaviour of antherozoids in the neighbourhood of 

 the oosphere, and of wandering gametes and antherozoids in the 

 neighbourhood of oogonia, we meet with the. most definite asser- 

 tions, that the sexual cells always exert a certain influence upon 

 one another, which makes itself felt over a certain distance, and 

 which always tends to induce the union of the two. This occur- 

 rence is the more remarkable, in that this mutual attraction 

 immediately disappears after fertilisation has taken place." 



The question naturally arises as to what are the forces to which 

 the phenomena can be attributed. Pfeffer has expressed the 

 view, based upon the above-mentioned experiments (p. 117), that 

 in the objects examined by him the antherozoids are attracted to 

 the egg-cells by chemical substances, which the latter secrete. Too 

 great an importance, however, must not be attached to these 

 opinions, as would be the case if we considered that the conjuga- 

 tion of two sexual cells was explained by them. In my opinion, 

 the chemical substances, which are secreted by the egg-cells, only 

 exert a secondary influence upon fertilisation ; they play a part 



