Key to the Species 



Colony with 64-128 cells about half of which 



are smaller and vegetative P. calif ornica 



Colony with 32-64 cells, only 4 of which are 



smaller and vegetative P. illinoisensis 



Pleodorina calif ornica Shaw 1894, p. 282 

 PL 2, Fig. 1 



Colony spherical, containing as many as 128 globose cells, about 

 half of them vegetative and half reproductive in function, the latter 

 distinctly larger than the former. Flagella subparallel within the mu- 

 cilage, diverging widely outward. Vegetative cells 6-14;u, in diam- 

 eter; reproductive cells up to 34ju, in diameter. 



Rare in the plankton of several lakes; occasionally abundant in 

 water rich in organic matter^ Mich., Wis. 



Pleodorina illinoisensis Kofoid 1898, p. 274 

 [Eudorina illinoisensis (Kofoid) Pascher] 



PI. 2, Fig. 3 



Colony globose, containing 32-64 cells, 4 of which are small and 

 vegetative, and located toward the posterior pole of the colony. 

 Vegetative cells 8-10/i, in diameter; reproductive cells 14-20/i, in 

 diameter. 



Rare; found in a fish hatchery pond. Wis. 



VOLVOX Linnaeus 1758, p. 820 



Colony free-swimming, spherical or ovate, composed of from 500 

 to several thousand cells arranged at the periphery of a gelatinous 

 sphere of homogeneous mucilage, in which, however, the individual 

 cell sheaths may be distinct; the cells all directed outward and each 

 having 2 flagella of equal length. In some species, the cells are inter- 

 connected by protoplasmic strands or 'canals'. Chloroplast a parietal 

 incomplete cup covering most of the cell wall. Daughter colonies 

 form within the interior of the sphere by repeated division of special 

 gonidial cells which have withdrawn from peripheral layer. Sexual 

 reproduction oogamous; female gametes large spherical cells within 

 the sphere; male gametes spindle-shaped, formed in several to many 

 rectangular plates or bundles in the interior of the colony, the 

 antherozoids with their longitudinal axes at right angles to the 

 surface plane of the plate. Zygote thick-walled, smooth, or bearing 

 external decorations such as spines and warts. 



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