FERTlLlSATKtN OF THE EGGS OF ANIMALS. 149 



According- to Strasbnrger^ they excrete a substance which 

 attracts the spermatozoa from a distance equal to two 

 diameters of an egg. On the other hand, the observations 

 and experiments by Bordet" upon the fertilisation of the eggs 

 of several species of Fucus led him to entirely negative 

 conclusions as regards a chemotactic attraction, while he 

 found that the spermatozoa were highly sensitive to contact. 

 According to this observer it is simply the ability of the 

 spermatozoa to adhere to surfaces by the tip of one of their 

 two cilia, which leads to their collection upon an egg, while 

 their meeting with it is simply a matter of chance. A few obser- 

 vations of my own at Naples upon the fertilisation of Cysto- 

 cyra barbata (one of the Fucaceae) did not reveal to me any 

 certain attraction of the spermatozoa from a distance, but the 

 collection of the spermatozoa upon the eggs in consequence of 

 their ability to cling to surfaces was clearly seen. Neverthe- 

 less, in view of the positive statement of Strasburger, a careful 

 reinvestigation of the question seems to me desirable. 



The other cases^ of supposed attraction of spermatozoa to 

 the egg-cells of plants all await a critical study. 



In the cases of Clamydomouas and of Ulothrix,* Pfeffer 

 has observed that the meeting of the swarm -spores, which 

 afterwards copulate, is purelj' a matter of chance. He also 

 found that the spermatozoa of a bull'' were not attracted by 

 meat extract. 



At present, to the best of my knowledge, not a single case 

 is known where chemotaxis plays a role in the fertilisation of 

 the eggs of animals. 



Dewitz^ has shown that the spermatozoa of certain insects 



> Strasburger, ' Das \wi . I'rakticuni,' 2 Aufl., 1SS7, p. 402. 



■' Bnrdct, "Contribution u I'Eliide de I'lrritabilile des Spcrniatozuides cliez 

 les Fucacecs," ' l^uli. de I'Acad. Belgique,' 8c ser., tome xxvii, 1894, p. SS9. 



3 See Pfeffer, loc. cil., i)|). 41(3—449. 



^ Loc. cit., p. 447. 



^ Loc. cit., p. 449. 



'' Dewitz, " Ueber GesctzniJissigkeit in (ier Ortsveriindcrnng dor Spernia- 

 tozoen und in der Vcreinij^iing derselbcn niit deni Ki," ' Arcli. 1'. tiic t;osaMunte 

 Phvsinloeir." Hd. xxxviii, ISSn. n. ;^5.S. 



