192 Chlorophycece 



& G. S. West 1 ] possesses a colony of four ovoid cells, each of which is 

 11-519 p. in length and 7'5 15'5 p. in breadth ; fig. 75 B F. The anterior 

 extremity of each cell is somewhat protracted and the cilia are only vibratile 

 towards their extremities, the movements of the coenobium being correspond- 

 ingly sluggish. It is a much rarer plant than G. pectorale and prefers the 

 open water of large ponds and lakes. It may possibly be identical with G. 

 sociale (Duj.) Warming, but it appears to differ in the grouping of the cells 

 and in the nature of the cilia. 



Genus Stephanosphaera Cohn, 1852. The coenobium consists 

 normally of eight cells arranged in an equatorial zone within a 

 tough, spherical or ellipsoidal investment. Occasionally young 

 coenobia are observed which contain only one or two cells. The 

 cells are ovoidal, and in the vegetative condition they possess 

 several green or colourless protoplasmic processes. The zone of 

 cells is situated rather towards the posterior pole of the coenobium 

 and the cilia, of which one pair is attached to the anterior pole of 

 each cell, penetrate the mucous investment in the equatorial plane. 

 The chloroplasts are rather irregular and contain from one to 

 several pyrenoids. Multiplication occurs by the division of each 

 cell of the coenobium, after having assumed a more or less globular 

 form, into four or eight daughter-cells, each group forming a new 

 coenobium. Sexual reproduction occurs by the fusion of isogamous 

 gametes, 8, 16, or 32 of which are formed from the division of 

 a single cell. The gametes are fusiform in shape, conjugating 

 laterally to form spherical ' zygozoospores ' which soon become 

 quiescent and of a yellowish-brown colour. 



St. pluvialis Cohn, which is the only species of the genus, is known to 

 occur both in England and Ireland. It is one of the scarcest of the Volvo- 

 cacese and is usually found in the rain-water which collects in the hollows of 

 rocks. The cells are 6 12 p. in diameter and the colonies 26 60 p.; 

 fig. 76 K. 



Genus Pandorina Bory, 1824. The coenobia are spherical or 

 subspherical and usually contain 16 cells closely packed within the 

 mucous investment. Sometimes coenobia of 8, or rarely of 32, 

 cells are observed. The cells are pyramidal in shape and reach 

 almost to the centre of the spherical colony, the pressure of 

 contact often causing them to become quite angular. Two widely 

 divergent cilia are attached to the broad end of each cell. Multi- 

 plication takes place by the formation of 16-celled coenobia from 

 each of the cells of the mother-coenobium. The daughter-coenobia 



1 West & G. S. West in Journ. Roy. Micr. Soc. 1896, p. 160, t. iii, f. 113. 



