OF MICRO-ORGANISMS. 8i 



ovule and the spermatozoid; the peripheral substance 

 of the ovule is seen to lift itself up in front of the sper- 

 matazoid in the shape of a minute protuberance; this 

 protuberance, at first, has a rounded shape, then it 

 grows thinner and forms a point which advances to- 

 wards the spermatozoid; this point is called the cone 

 of attraction (see Fig. 8). The head of 

 the spermatozoid fastens itself upon the 

 cone, which seems to draw it into its in- 

 terior. The tail of the spermatozoid does 

 not appear to enter into the interior of 

 the ovule and take part in the process of 

 ■• ■.;.°;«;-- fecundation, which consists simply in the 

 Fig. 8.—K small fusion of the head of the spermatozoid 



portion of the ovule . . , , ^ . n i 



of a star-fish i,Aste- With the nucleus oi the cellule. 



ri as gl aci alls') 



showing the forma- As soon as the head of the spermato- 



tion of the cone of , , - , , .. , j.i 



attraction. (Ac- zoid has penetrated into the ovule, the 



cording to Fol.) -4. ir • ^ l i 



latter enwraps itself m an envelope, to 

 protect itself against the other male elements. It ap- 

 pears, in fact, to be well settled that the penetration 

 into the vitellus of several spermatozoids marks the 

 beginning of an adverse change: the subsequent seg- 

 mentation of the ovule is irregular, and development 

 ceases. 



The membrane in which the fecundated ovule of 

 the Asterias glacialis infolds itself, is formed by a con- 

 densation of the peripheral layer of the vitellus; the 

 condensation starts from about the point where the 

 spermatozoid penetrated, and gradually spreads over 

 the whole surface of the ovule; the formation of this 

 protective membrane is so rapidly effected, that access 

 to the ovule is barred against spermatozoids who might 

 be only a few seconds behind the first one. 



Sexual selection, then, acts among spermatozoids 



