286 



THE CELL 



in other respects are absolutely similar, may be called female, 

 since it remains at rest, and must be sought for by the other for 

 the purposes of conjugation. Thus a relationship, similar to that 

 seen in Ph&eosporese and Cutleriaceas, is produced. 



In some species of Phseosporese, the male and emale swarm- 

 spores cannot be distinguished from one another when they are 

 evacuated from the mother-cell ; they are of the same size, and 

 are each provided with a pigment spot and two flagella ; they 

 do not pair whilst they are swimming about. However, a 

 difference between the gametes soon becomes apparent. Some 

 come to rest earlier than others ; each of these attaches itself by 

 the point of one of its flagella to some solid object, to which it 

 draws up its protoplasmic body by shortening and contracting 

 the connecting flagellum ; it then retracts its second flagellum. 

 These resting swarm-cells may be termed female ; their capacity 

 for becoming fertilised is only retained for a few minutes ; they 

 appear to exert, as Berthold expresses it, "a powerful attraction " 

 upon the male gametes, which are swimming about in the water, 

 so that in a few seconds one egg may be surrounded by hundreds 

 of swarm-spores, one of which fuses with it (VII. 51). 



Sexual differentiation is still more marked in Cutleriacese. Here 

 the sexual swarm-cells become different in size before they are 

 separated from the parent, the female one developing singly, and 

 the male in groups of eight. In this genus the difference in size 

 of the sexual cells is fairly striking. Both kinds of gametes 

 swim about in the water for a time ; fertilisation, however, can 

 only occur after the female swarm-spore has come to rest, has 

 drawn in its flagella, and has become spherical. Upon the egg, 

 which is now capable of becoming fertilised, a hyaline spot 

 appears, which was produced by the drawing in of the anterior 

 beak-like end. This is the so-called reception spot. It is the 

 only point at which one of the small male swarm-spores, which 

 soon come to rest around the female cell, can fertilise it. When 

 fertilisation is complete, the zygote surrounds itself with a 

 cellulose cell-wall. 



In Fucacese, Characeas, and other Algae the difference is still 

 more marked than in Cutlerlaceas. Here the female cells, which 

 attain a considerable size, do not even pass through the swarm- 

 spore stage. They are either expelled to the exterior in a mature 

 condition as globular immotile egg cells (Fucacess, Fig. 156 G), 

 or they are fertilised at the place where they originated, that is, 



