xvr SEXUAL REPRODUCTION 173 



cell, the ovtfm 1 or egg-cell (D 4 , ov\ which, by the gelatiniza- 

 tion and subsequent disappearance of a portion of the wall 

 of the ovary, is in free contact with the surrounding water. 



At the same time the protoplasm of the spermary under- 

 goes multiple fission, becoming converted into numerous 

 minute green bodies (D 5 ), each with two flagella. called 

 sperms. 2 These are liberated by the rupture of the spermary 

 (D T ) at its distal end, and swim freely in the water. 



Some of the sperms make their way to an ovary, and, as 

 it has been expressed, seem to grope about for the aperture, 

 which they finally pass through (D 6 ), and are then seen 

 moving actively in the space between the aperture and the 

 colourless distal end of the ovum. One of them, and prob- 

 ably only one, then attaches itself to the ovum^and be- 

 comes completely united with it, forming the oosperm? a 

 body which we must carefully distinguish from the ovum, 

 since, while agreeing with the latter in form and size, it 

 differs in having incorporated with it the substance of a 

 sperm. 



Almost immediately the oosperm (D T , osp] surrounds itself 

 with a cellulose wall, and numerous oil-globules are formed 

 in its interior. It becomes detached from the ovary, and, 

 after a period of rest, germinates (E 1 , E 2 ) and forms a new 

 Vaucheria plant. 



It is obvious that the fusion of the sperm with the ovum 

 is a process of conjugation in which the conjugating bodies 

 differ strikingly in form and size, one the megagamete or 

 ovum being large, stationary, and more or less amoeboid : 

 the other the microgamete or sperm small, active, and 



1 Frequently called oosphere. 



2 Often called spertnatozooids or antherozooids. 



3 Often called oo spore. 



