174 Volvocineae 



chloroplast without a pyrenoid ; they are very minute and furnished with two 

 very long cilia (fig. 97 A F). This organism is also peculiar in moving 

 backwards, the body of the cell being pushed in front by the movements of 

 the cilia which are carried behind. 



Polytoma uvellu Ehrenb. (fig. 102 A D) is a colourless saprophytic 

 member of the Chlamydomonadea? in which, although as a rule there is no 

 chromatophore-stroma, starch -grains are stored in the cell. The cells divide 

 while in the motile state, and the daughter-cells are facultative gametes. 



The Chlamydomonadese occur most abundantly in stagnant water, especially in the 

 spring months. They prefer rain-water, and arc often found in great abundance in water- 

 butts, tanks, small pools, and in canals, frequently giving a decided green colour to the 

 water. 



The genera are: Chlamydomonas Ehrenb. 1832 [iuclus. Chloromonas Gobi, 1900 * and 

 Dangeardia Bougon, 1900] ; Polytoma Ehrenberg, 1831 ; Brachiomonas Bohlin, 1897 ; 

 Lobomonas Dangeard, 1899 ; Agloe Pascher, 1912 ; Scourfieldia (I. S. West, 1912. It is 

 possible that Oloeomonas Klebs and Kleiniella France (1894) should also be added, but 

 at present we know little about these genera. 



Sub-family PHACOTE.E. This small group is only distinguished from the 

 Chlamydomonadese by the possession of a strong thick wall around each 

 vegetative cell. In both Pteromonas and Pltacotus the cells are compressed 

 as in Scherffelia in the Carteriacea 1 and Scourfieldia among the Chlamy- 

 domonadese. Reproduction is only known to occur by the longitudinal 

 division of the motile cells. The wall of Pteromonas is closely adherent 

 except along the line of greatest circumference, where it projects laterally as 

 a wing-like expansion except at the anterior end of the cell at the point 

 where the cilia are attached (fig. 97 G J). In Phacotus (fig. 101 G and H) 

 the thick wall, which is calcified and externally sculptured, is outstanding all 

 round the cell, and consists of two loosely connected plates which separate on 

 the escape of the daughter-cells. 



It is probable that Coccomonas should be included in this sub-family, since 

 it is a Chlamydomonad with a hard outstanding cell-wall, which is sometimes 

 four-angled. 



The genera are : Phacotus Perty, 1852 ; Coccomonas Stein, 1878 ; Pteromonas Seligo, 

 1886. A colourless form is seen in Chlamydoblepharis France, 1892 (fig. 102 .fi'and F). 



Sub-family VOLVOCE/E. The Algse of this sub-family consist of a motile 

 cosnobium of Chlamydomonadine cells generally embedded in a copious and 

 lefinite mucilaginous envelope of relatively firm consistency. The cells, in all 

 except certain species of Volvox, are to a great extent independent units of 

 the colony and not in any way protoplasmically connected. The two cilia of 

 each cell project outside the colony, passing through minute canals in the 

 mucous envelope, although in Gonium, in which the amount of mucus is 



1 Vide G. S. West, '12, p. 32s. 



( 



