FERTILISATION OF THE EGGS OF ANIMALS. 1G7 



VII. The Direction of Peneteation of the Gelatinous Coat. 



FoP observed for Asterias tbat when a sperraatozooii had 

 come in contact with the gelatinous coat it placed itself 

 perpendicular to it,, and then penetrated radially to the egg, 

 meeting aud fusing when half-way through with a curious 

 "cone d'exudation." Fol concluded that the gelatinous 

 coat is an apparatus for catching the spermatozoa when they 

 come in contact with it, aud attributed the radial structure to 

 lines of more or less resistance, which serve to guide the 

 spermatozoa directly to the egg. 



Selenka- investigated the development of the gelatinous 

 coat, and found that at first it is penetrated by fine radial 

 protoplasmic filaments, each in its own canal. Later the fila- 

 ments become withdrawn, but the canals remain until after 

 fertilisation. Seleuka also observed that the spermatozoa 

 penetrate the jelly "always in a radial direction,'^'^ and stated 

 that this is due to the spermatozoa making their way through 

 the canals. This explanation appears to be very plausible. 

 Before, however, accepting it as being sufficient, we shall do 

 well to bear in mind the observations of Kupffer and Benecke 

 upon the fertilisation of the eggs of Petromyzon. 



According to the last-named authors the spermatozoa of 

 Petromyzon penetrate a thick gelatinous dome covering 

 one end of an egg in a radial direction.* This observation, 

 upon which special stress was laid, confirmed the statements 

 previously made by August Miiller. Although the inner 

 shell-layer was found to contain radial canals, Kupffer and 

 Benecke could discover no trace of such in the outer shell- 

 layer, while they described and figured the dome as beiug 



^ Fol, ' Reclierclies sur la Fccoiidat.ion, etc.,' 1S79. 



- Selt'iika, ' Zoologisclie Studien, Bel'ruclitung des Eies von Toxopiiciislcs 

 variegatus,' 1S78, ]>. 2. 



* Loc. cit., |). 5. 



* Kujjffer and Benecke, ' Der Vorgang der Befiuchtung am Ei dcr Neu- 

 naugen,' Konigsberg, 1878, p. 11. 



