THE ALGAE 65 



to form a hollow coenobium. This is liberated as a new colony after the 

 breakdown of the parent cell. This inversion of the daughter colonies during 

 development should be compared with that described in Eiidorhia and Volvox. 

 The liberation of independent zoospores rarely occurs. 



Sexual reproduction consists in the liberation of the naked protoplasts of 

 the cells, which escape from the membranes and become the gametes. Con- 

 jugation is usually isogamous, but there is a tendency towards a preferential 

 fusion of gametes of unequal size, thus showing an advance towards anisogamy, 

 which becomes much more pronounced in Eudorina and Volvox. 



The zygote germinates to liberate a single zoospore, which divides to form 

 a new colony. Four cells are actually formed by the germinating zygote, 

 but only one of these survives to form a zoospore, while the other three 

 abort. This suggests that meiosis probably occurs at this stage, as in Goniiim. 



Eudorina 



In Eudorina the colony is larger than in Pondorina. It is oval in shape 

 and consists generally of thirty-two globose cells, loosely arranged on the 

 peripher\' of a hollow mucilaginous 

 matrix (Fig. 41). The biflagellate 

 cells are of the typical chlamydo- 

 monad type, but the chloroplast often 

 has several pyrenoids and the cells 

 show a progressive reduction in the 

 size of the eye-spot as we pass from 

 the anterior to the posterior end of 

 the colony. Unlike Pandorina, the 

 cells forming the colony are con- 

 nected together by extremely fine ^^^ ^,.-Eudorh,a. Colony in surface 

 protoplasmic strands, only visible and in optical section. 



after special staining. The flagella 



are long and pass outwards from the cells through minute open funnels 

 in the mucilage investment (Fig. 40, m). 



Reproduction 



Asexual reproduction (Fig. 42) consists in the formation of daughter 

 colonies within the individual parent cells, whose protoplasts divide up into 

 a number of parts equal to the number of the cells of the new colony (Fig. 

 43). The young colony is at first flat, but finally curls over to form a hollow 

 sphere. This new colony is liberated by the breakdown of the parent cell 

 wall. As all the cells reproduce simultaneously in this way the parent colony 

 naturally disappears after reproduction. 



Sexual reproduction is more complex than in Pandorina and shows a 

 definite advance, to oogamy, the gametes being quite distinct in appearance 

 and behaviour. The colonies are generally dioecious, that is to say, the 

 male and female gametes are formed in difl'erent colonies. In the female 



\ie\v 



