Key to the Species 



1. Colony of from 8000 to 17,000 cells which are angular, 



polygonal, or stellate in end view V. globator 



1. Colony with fewer cells than above; cells round in end view _ 2 



2. Colony of 1300-3200 cells which are not inclosed by 



individual sheaths V. aureus 



2. Colony smaller, 500-2000 cells, inclosed by individual sheaths V. tertius 



Yolvox aureus Ehrenberg 1838, p. 71 

 PL 2, Fig. 4 



Dioecious (rarely monoecious), spherical colonies of (500)- 

 1300-3200 ellipsoidal cells, 4-6/x in diameter, with interconnections 

 of fine protoplasmic strands; individual cell sheaths wanting. Strands 

 of mucilage radiate from the center of the colony. Cells contain a 

 circular, parietal plate-like chloroplast, with 2 contractile vacuoles 

 at the anterior end, below the point of flagella attachment, and a 

 pigment-spot, anterior and lateral. In mature coenobia, 2 or more 

 daughter colonies are present. As many as 21 (usually about 9) eggs 

 are formed in female colonies; half of the cells in male coenobia 

 develop antherozoid bundles, 15-18/i, in diameter, with as many as 

 32 antherozoids in each bundle. Zygote 38-62/i, in diameter, with a 

 smooth wall. 



Common in the plankton of many lakes; sometimes abundant in 

 shallow, backwater habitats; also found in inlets to lakes where 

 water is slow-flowing or pooled. Mich., Wis. 



Volvox globator Linnaeus 1758, p. 820 

 PI. 2, Fig. 5 

 Large, monoecious, spherical or ovate, gelatinous colonies contain- 

 ing as many as 17,000 ovoid or pyriform cells. Cells 2.5-3.5/a in di- 

 ameter, with conspicuous protoplasmic interconnections; with 1 

 parietal plate-like chloroplast and a pigment-spot in each cell, and 

 with 2-6 small contractile vacuoles in the anterior region below the 

 point of flagella attachment. Individual sheaths of the cells conspic- 

 uous and not confluent with the colonial mucilage, clearly visible in 

 surface view of the colony, the sheaths 5-8-sided from mutual com- 

 pression. Coenobium commonly containing 4-7 (or as many as 17) 

 daughter colonies; sexual colony with 11-17, or up to 40, eggs, each 

 inclosed by a vdde gelatinous sheath; 3-7 rectangular plates of fusi- 

 form antherozoids in bundles of 64-256, 22-32^ in diameter. Zy- 

 gotes 45-54/i, in diameter, with thick walls exteriorly decorated wdth 

 wart-like, blunt spines and verrucae. 



[78] 



