436 Illinois State Laboratory of Natural History. 



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KEYS TO THE GENERA AND SPECIES OF THE SUBFAMILY 



VOLVOCIN^. 



Cells arranged in ccenobia of definite forms varying with 

 the species, biflagellate, with stigma and one or more chro- 

 matophores; surrounded by a gelatinous envelope whose 

 development separates them to a greater or less degree; 

 number not uniform, varying in the different species, often, 

 but not always, definite. Asexual reproduction by repeated 

 divisions of gonidial cells, which constitute the whole or only 

 a part of the parental organism, to form daughter organisms ; 

 sexual reproduction in some species (in others unknown) by 

 the conjugation of male and female gametes, resulting in the 

 formation of a resting stage which later develops into a new 

 organism. 



Genera. 



Cells arranged in form of plate with flagella upon 

 one face only. 2, 



Cells arranged in spherical, ellipsoidal, or flattened 



colonies, flagella not confined to one face. 3. 



Cells in a squarish plate, envelope closely adherent. 



Gonium. 



Cells in a rounded plate, envelope swollen, oval, or 

 spherical. Stephanosphcera. 



Colony ellipsoidal or spherical, cells crowded to- 

 gether, conical, reaching towards center, outer 

 membrane of concentric layers. Pandorina. 



Cells not crowded together, nor reaching towards 

 center of colony. 4. 



Colonies ellipsoidal or flattened, cells uniform in 

 size. 5. 



Colonies spherical or spheroidal, or, if ellipsoidal, 



with small vegetative and large gonidial cells. f>. 



Colony ellipsoidal or spherical, poles not differen- 

 tiated by arrangement or size of cells, or by struc- 

 ture of envelope. Eudorina. 



Colony flattened, horse-shoe-shaped, with poles dif- 

 ferentiated by arrangement of cells, posterior end 

 with tails. Platydorina. 



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