io8 



Aquatic Organisms 



and a singularly persistent bad flavor, and under such 

 circumstances it becomes a pest in water supplies. 



Glenodinium (fig. 30/), Peridinium, and Ceratium 

 (fig. 307) are three brownish shell-bearing flagellates of 

 wide distribution often locally abundant, especially in 

 spring and summer. These all have one of the two long 

 flagella laid in a transverse groove encircling the body, 



the other flagellum free (fig. 33). 

 Glenodinium is the smallest, 

 Ceratium, much the largest. 

 Glenodinium has a smooth 

 shell , save for the grooves where 

 the flagella arise. Peridinium 

 has a brownish chitinous shell, 

 divided into finely reticulate 

 plates. Ceratium has a heavy 

 grayish shell prolonged into 

 several horns. 



On several occasions in spring 

 we have seen the waters of the 

 Gym Pond on the Campus at 

 Lake Forest College as brown 

 as strong tea with a nearly pure 

 culture of Peridinium and con- 

 currently therewith we have 

 seen the transparent phantom-larvag of the midge 

 Corethra in the same pond all showing a conspicuous 

 brown line where the alimentary canal runs through 

 the body, this being packed full of Peridinia. 



Trachelomonas (fig. 30 d) is a spherical flagellate hav- 

 ing a brownish shell with a short flask-like neck at one 

 side whence issues a single flagellum. This we have 

 found abundantly in pools that were rich in oak leaf 

 infusions. 



FlG. 33. Ceratium (The trans- 

 verse groove shows plainly, 

 but neither flagellum shows 

 in the photograph.) 



