48 PROTOCOCCOIDE^;. 



coll. The vegetative reproduction takes place by the division of 

 all, or a few, of the cells of the individual ; in some a palmella-stage 

 is found in addition. The sexual reproduction takes place by 

 isogamous or oogamous fertilisation. 



The Volvocaceae may be considered to include the original forms of the Chloro- 

 phyceae. because, among other reasons, the motile stage is here the most promi- 

 nent; they also form the connecting link between the animal Flagellata, and 

 forms intermediate to the Syngeneticte may perhaps be found amongst them. 

 Three series of green Alga? may be supposed to have taken their origin from the 

 Volvocaceae : CONJUGATED (Desmidiacea) which have lost the swarming stage, but 

 whose conjugation is the nearest to the fertilisation in Chlamydomonas pulvis- 

 ciilus : the PROTOCOCCACE.E in which the vegetative divisions have disappeared, 

 while the swarming stage continues to be present, though of shorter duration ; 

 and TETRASPORACE.S:, in which the vegetative divisions are more prominent, 

 whilst the swarming stage is less so. 



A. UNICELLULAR INDIVIDUALS. The principle genera are : 

 mydomonas, Sphcerella, Phacotus. Sphcerella nivalis is the Alga 

 which produces the phenomenon of " Red Snow," well known en 

 high mountains and on ice and snow fields in the polar regions. 

 The red colouring matter which appears in this and other green 

 Algas, especially in the resting cells, is produced by the alteration 

 of the chlorophyll. 



Phacotus lenticularis has an outer covering incrusted with lime, 

 Avhich, at death, or after division, opens out into two halves. 

 Species may be found among Chlamydomonas, in which conjuga- 

 tion takes place between gametes of similar size without cell-wall, 



but in C. pulvisculus conjugation 

 takes place between male and 

 female aplanogametes which are 

 surrounded by a mucilaginous 

 envelope. 



B. MULTICELLULAR INDIVIDUALS, 



The most important genera are 

 Gonium, Stephanosphcera, Pandor- 

 ina, Eudorina, Volvox. Gonium 

 has 4 or 16 cells arranged in a 



definite pattern in a flat plate 

 Fig. 41 Gonium pectorale. /Ti1 . . .. ^ 7 . / - ri . . , 



(Fig. 44). Pandonna (Fig. 45), 



has 16 cells arranged in a sphere (Fig. 45 A). The vegetative 

 reproduction takes place in this way : each cell, after having 

 rounded off, and after the withdrawal of the cilia, divides itself 



