CEDOGONIUM 45 



is developed into a long hair. The ordinary cell has 

 a wall of cellulose lined interiorly with the primordial 

 utricle, a large chloroplast including some pyrenoids, 

 a central vacuole containing cell sap, and a good- 

 sized nucleus planted in the primordial utricle. The 

 thallus grows in accompaniment with the increase of 

 the ordinary cells by division. Asexual reproduction 

 is effected by means of zoospores, as in Ulothrix, 

 and any ordinary cell may develop into a single 

 zoospore. In this development the cell-contents draw 

 away from the cell-wall, become rounded off, and 

 escape through a crack in the wall, as shown in 

 Fig. 14, A. The resulting zoospore (Fig. 14, B) is a 

 naked protoplasmic body, egg-shaped, transparent at 

 the smaller end, around which there is a fringe of cilia, 

 and containing a nucleus and chloroplast. On escape 

 from the mother-cell, it swims about, ciliated end fore- 

 most, for a short time. It ultimately comes to rest, 

 attaching itself by its colourless end to some object. 

 The cilia rapidly disappear, the protoplasm secretes a 

 cell-wall, the cell divides, and the zoospore gives rise to 

 an ordinary filament or thallus. 



We have seen that in Ulothrix sexual propagation 

 arises from the fusion of gametes of similar size and 

 sexually undifferentiated ; they are both free-swimmers. 

 In (Edogonium the male and female gametes are distinct, 

 the former being smaller than the latter, while the male 

 is active and the female passive. The term " gamete " 

 is, strictly, applied only to similar sexual cells; where 

 sex distinction is apparent the female cell is called the 

 " egg " and the male the " spermatozoid." The egg of 

 (Edogonium is formed from a special cell of the thallus, 



