98 WISCONSIN PHJTOPLANKTON 



one eyespot, and a cup-shaped to disciform chloroplast that contains 

 one pyrenoid. Number of cells in a colony varying from 200-22,000. 



Asexual reproductive cells few in number (rarely more than 20) and 

 forming autocolonies by repeated division, the young colonies migrat- 

 ing to the center of the coenobe at a certain stage in their development. 



Sexual reproduction heterogamous, monoecious or dioecious, with a 

 development of 6-400 cells into spherical oospheres and few or many 

 of the cells into antheridia that contain 16-256 biciliate fusiform anther- 

 ozoids. Zygote with a smooth or stellate wall. 



KEY TO THE SPECIES. 



Cells with cytoplasmic connections. 



Cytoplasmic connections heavy ,- V. GLOBATOR 



Cytoplasmic connections delicate V. ATTREUS 



Cells without cytoplasmic connections V. MONONAE 



VOLVOX GLOBATOR L. PI. 18, Figs. 3-5. 



Systema natura, Ed. 10: 820. 1758; Cohn, Beitr. z. Biol. d. Pflanzen 1, Heft 3: 

 93, pi. 2, figs. 1-6. 1875. 



Colonies large, with many (1,000-22,000) cells that are flattened and 

 pentagonal to octagonal in surface view. Cells connected to one an- 

 other by stout cytoplasmic strands. Chloroplast of cells single, flat- 

 tened and angular, with one pyrenoid. Cells with 2-6 contractile vacu- 

 oles at the base of the two cilia and with an eyespot. Gelatinous sheaths 

 of individual cells sharply defined and (in surface view) pentagonal 

 to octagonal by mutual compression. Generally with 8 asexual repro- 

 ductive cells giving rise to autocolonies. Colonies commonly monoe- 

 cious, with 12-40 (generally 20-30) oospheres enclosed by large gelat- 

 inous vesicles. Antherids a flat plate of 64-256 fusiform antherozoids 

 with laterally attached cilia. Zygote verrucose, with conical warts. 

 ( Tychoplanktont) . 



Cells 2-7.5 (generally 3-5) ^ in diam. Colonies 400-800 //, in diam. 



Center (s), Hooker (rr), Kegonsa (rr), Monona (r), Soft (rrr), Waubesa 

 (rrr). 



VOLVOX AUREUS Ehrenberg. PI. 18, Fig. 2. 



Die Infusionsthierchen 71, pi. 4, fig. 2. 1838; Klein, Jarhb. f. wiss. Bot. 20: 

 138, pi. 12, figs. 26-33. 1889. 



Colonies spherical, containing a comparatively small (200^,000) 

 number of cells. Cells circular in surface view, connected with one 

 another by very fine cytoplasmic strands. Individual gelatinous sheaths 

 of cells confluent with the colonial envelope. Cells containing a spheri- 



