No. IO.] FRESH- WATER ALG.E. 4 1 



Volvox Ehrb. Coenobium spherical, hollow, the surface 

 composed of green cells estimated as high as 22,000, arranged 

 regularly on the wall, and each provided with two cilia, which 

 reach through the gelatinous covering and keep the ccenobium 

 in constant motion. Each green cell is attached to the six sur- 

 rounding ones by fine threads which are difficult to see even 

 under high power and with favorable light. Oogonia and 

 anthcridia are developed from vegetative cells, and a brown, 

 smooth or star-shaped cell is often found which is supposed to 

 be a fertilized oospore in a resting stage. Asexual reproduc- 

 tion takes place by the division of the larger vegetative cells, 

 which form new families. These after sufficient growth 

 separate from the mother-cell and begin life independently. 



V. aureus Ehrb., Fig. 75. 



V. globator (L.) Ehrb., Fig. j6. Fig. 74 is a fertilized 

 oospore. These are frequently found within the ccenobia, and 

 also occur free in the water. Ehrenberg named it V . stellata, 

 but of course this was an error. 



Spondylomorum Ehrb. (Uvella Ehrb.; Phacolomonas 

 Stein.). Ccenobium of sixteen cells in four alternating rows, 

 each cell with four cilia. 



6\ quateriiariuiu Ehrb., Fig. 288. 



Stephanosphaera Cohn. Eight green cells, each having 

 two vibrating cilia, are arranged at regular intervals in an 

 equatorial circle, enclosed in a colorless sphere. Propagation 

 by macrogonidia, formed by eight-fold division of the green 

 cells, each bearing two cilia and a lateral red spot, and gathered 

 into families of eight ; or by microgonidia, each provided with 

 four cilia, formed by repeated division, and at first revolving 

 within the common sphere, afterwards escaping singly. In 

 hollow rocks and pools after rain. 



Eudorina Ehrb. (Eudorinella Lemmermann). Cceno- 

 bium somewhat oval or spherical, composed of 16 or 32 globular 

 green cells, each with two cilia, arranged around the color- 

 less sphere at nearly regular intervals. Usually four of the 

 32 cells develop antheridia and the rest oogonia for the sexual 

 reproduction. Asexual reproduction by the division of the 

 cells into 16 or 32 parts to form daughter-ccenobia. 



E. elegans Ehrb., Fig. 285. 



