226 PROTOZOOLOGY 



Genus Volvox Linnaeus. Often large spherical or subspherical 

 colonies, consisting of a large number of cells which are differen- 

 tiated into somatic and reproductive cells; somatic cells numerous, 

 embedded in gelatinous matrix, and contains a chromatophore, 

 one or more pyrenoids, a stigma and several contractile vacuoles; 

 in some species protoplasmic connections occur between adjacent 

 cells; generative cells few and large. Both mono- and bi-sexual re- 

 productions occur; monosexual gametes usually fewer and larger in 

 size than bisexual ones, each producing a young colony by repeated 

 division; bisexual reproduction anisogamy; zygotes usually brown- 

 ish red in color, with smooth, undulating, or spinous envelopes; fresh 

 water. Many species. Smith (1944) made a comprehensive study of 

 the known species. 



V. globator L. (Fig. 99, a). Monoecious. Sexual colonies 350-500m 

 in diameter; 5000-15,000 cells, with cytoplasmic connections; 3-7 

 microgametocytes, each of which develops into over 250 microgam- 

 etes; 10-40 macrogametes; zygotes 35-45m in diameter, covered with 

 many sharply pointed spines. Partheno genetic colonies 400-600/x in 

 diameter; 4-10 gonidia, 10-13ju in diameter; young colonies up to 

 250m. Europe and North America. 



V. aureus Ehrenberg (Figs. 72; 99, h). Dioecious. Male colonies 

 300-350ju in diameter; 1000-1500 cells, with cytoplasmic connec- 

 tions; numerous microgametocytes; clusters of some 32 microgam- 

 etes, 15-18m in diameter. Female colonies 300-400^; 2000-3000 

 cells; 10-14 macrogametes; zygotes 40-60ju with smooth surface. 

 Parthenogenetic colonies up to 500/x; 4-12 gonidia; young colonies 

 150)u in diameter. Europe and North America. 



V. tertius Meyer. Dioecious. Male colonies up to 170/x in diameter; 

 180-500 cells, without cytoplasmic connections; about 50 micro- 

 gametocytes. Female colonies up to 500jLt; 500-2000 cells; 2-12 

 macrogametes; zygotes 60-65^ with smooth wall. Parthenogenetic 

 colonies up to 600m in diameter; 500-2000 cells; 2-12 gonidia. Europe 

 and North America. 



V. spermatosphaera Powers. Dioecious, Male colonies up to 100m 

 in diameter; cells, without connection, up to 128, each becoming 

 microgametocyte. Female colonies up to 500m in diameter; 6-16 

 macrogametes; zygotes 35-45m; with smooth membrane. Partheno- 

 genetic colonies up to 650m in diameter; 8-10 gonidia; young colonies 

 ellipsoid, up to 100m in diameter. North America. 



V . weismannia P. Dioecious. Male colonies 100-150m in diameter; 

 250-500 cells; 6-50 microgametocytes; clusters of microgametes (up 

 to 128) discoid, 12-15m in diameter. Female colonies up to 400m; 



