FERTILISATION 215 



Pfeffer's experiments l upon the spermatozoa of ferns are usually 

 cited as evidence of this view. 



Pfeffer observed that malic acid, when put into a capillary 

 tube with one end open and placed in a drop of liquid con- 

 taining fern spermatozoa, has a strong attractive influence upon 

 these organisms, causing them to swim in large numbers into 

 the opening of the tube. He concluded, therefore, that it is 

 the malic acid in the archegonium of the fern's ovum which 

 causes the approach of the spermatozoa. 



According to Strasburger, 2 the ova of the Fucacese also 

 possess chemotactic properties, attracting the spermatozoa from 

 a distance equal to about two diameters of an ovum. Bordet, 3 

 however, who likewise experimented upon the Fucaceae, 

 obtained no evidence of chemotactic attraction, but he found, 

 on the other hand, that the sperms were very sensitive to 

 contact. 



Jennings, 4 in the course of his experiments on the behaviour 

 of the Protozoa, has shown that these organisms will tend to 

 collect in a drop of acid placed in water. This is due to the fact 

 that, whereas no reaction takes place when the individuals pass 

 from water to acid, there is a distinct reaction in passing in the 

 reverse direction. All the organisms which enter the drop of 

 acid remain there, and consequently they accumulate, but this 

 is not due to any attractive influence on the part of the drop. 

 It is of course possible that Pfeffer's observations on the sup- 

 posed attraction possessed by malic acid for the spermatozoa of 

 ferns is susceptible of a similar explanation. 



Buller, 5 who has discussed the question at some length and 

 has performed numerous experiments, states that, so far as he is 

 aware, not a single case is known where chemotaxis plays a part 

 in the fertilisation of the ova of animals. 



1 Pfeffer, " Locomotorische Richtungsbewegungen durch chemische Reize," 

 Untersuchungcn aus. d. Bot. Inst. zur Tubingen, vol. i., 1884. 



2 Strasburger, Das botan. Prakticum, Berlin, 1887. 



3 Bordet, " Contribution a l'6tude de 1'Irritabilite des Spermatozoides 

 chez les Fuccacdes," Bull, de VAcad. Belgique, vol. xxxvii., 1894. 



4 Jennings, " Studies of Reactions to Stimuli in Unicellular Organisms, 

 Amcr. Jour, of Phys., vol. xxi., 1897. 



5 Buller, " Is Chemotaxis a Factor in the Fertilisation of the Eggs of 

 Animals?" Quar. Jour. Micr. Science, vol. xlvi., 1902. 



