144 



FRESH- WATER BIOLOGY 



72(71) Cells ellipsoidal or nearly spherical. ....... , ; . . . . . 73 



73 (74) Membrane widely separated from the chromatophore but connected 

 with it by protoplasmic strands. Two cilia present. 



Sphaerella Sommerfeldt. 



Chromatophore netted, with two or more pyrenoids and a pigment spot. 

 Asexual reproduction by longitudinal division, sexual by isogametes. A 

 palmella condition may occur. 



Sphaerella often assumes a red color, due to the presence of hemato- 

 chrome, and is reported in a few cases as being the organism causing "red 

 rain." It was also supposed that 5. nivalis caused the phenomenon of "red 

 snow," but the form described by Chodat shows the chloroplast as lying 

 close to the membrane, so this is probably a Chlamydomonas. 



FlG. 143- Sphaerella pluvialis Flotow. X about 600. (After Schmidle.) 



Membrane not separated from the chromatophore 75 



74 (73) 



75 (76) 



Two cilia and a pyrenoid present. 



Color rarely red. 



Chlamydomonas Ehrenberg. 



Cells ellipsoidal or spherical; chromatophore single, hollow, parietal; a pigment 

 spot and two cilia at the anterior end. Reproduction by vegetative division, also 

 by copulation of gametes which are either alike or slightly unlike as to size. Zygo- 

 spore green or red. The products of the vegetative division may pass at once into 

 a motile state with cilia, or may be non-motile, according to conditions in the sur- 

 rounding medium. 



FIG. 144. Chlamydomonas ohioensis Snow. X looo. (Original.) 



76 (75) Structure as in Chlamydomonas but with 4 cilia. Some include this 

 genus under Chlamydomonas Carteria Diesing. 



The shape of the cells in the different species differ rather more 

 than in Chlamydomonas ; the structure of the cells, however, is 

 identical, except for the cilia. Species also occur in much the same 

 localities as Chlamydomonas but are less frequent. 



FIG. 145. Carteria obtusa Dill. X about 475. (After Dill.) 



77 (70) Cells united to form a colony of definite shape which is constantly 



in motion 78 



78 (79) Colony not surrounded by a gelatinous envelop. 



Spondylomorum Ehrenberg. 



Colony of 16 cells loosely united, their anterior ends all pointing 

 toward one point. The cells are obovate, with 4 cilia at their 

 anterior ends, a pyrenoid, and a pigment spot. A new colony of 16 

 originates by successive division from a vegetative cell. 



FIG. 146. Spondylomorum qualernarium Ehrenberg. (After Stein.) 



79 (78) Colony surrounded by a gelatinous envelop 80 



80 (83, 88) Colony not spherical or spheroidal 81 



