Feb., 1920] The Protozoa of Mirror Lake 93 



height of water in this pipe varied from nine-sixteenths to one 

 and seven-eighths inches during the period of study. 



The shore of the larger pond is steep, and the soil of the bank 

 is firm as contrasted with the loose marshy earth around the 

 smaller pond. The distance from the ground level to the surface 

 of the water averages about one foot. 



The larger pond is shaded only at a few places along the 

 shore where there are overhanging trees. There is a white 

 poplar {Populus alba Linnaeus) just east of the spring, and its 

 alga-covered roots, which extend into the water, form a habitat 

 for many Protozoa. An alder tree {Alnus incanus Linnaeus) 

 shades the water just west of the spring. 



The goldfish {Carassius auratus Linnaeus) is very abundant 

 in this part of Mirror Lake. During the time when ice covered 

 the lake, these collected near the outlet of the spring, for here 

 the water never froze. At this point the caretakers occasionally 

 throw food (usually dry bread) to them. Tench {Tinea 

 tinea Linnaeus), carp (Cyprinus earpio Linnaeus), and minnows 

 (Lepomis pallidus (Mitchill) ) are plentiful, but occur in smaller 

 numbers than do the goldfish. Common brown rats {Mus 

 norvegieus Erxleben) and muskrats {Fiber zibethicus Linnaeus) 

 live in burrows along the shore. The water snake {Matrix 

 sipedon Linnaeus) was seen once. Frogs and crayfishes are 

 common. Algae were common during most of the period of 

 study. The most common were Spirogyra flimiatilis, several 

 species of Oedogonium, Scenedesmus quadricaiida, Pediastrum, 

 and Ankistrodesmiis. 



Descriptions of the Stations. 



station a. 



Sediment on decaying leaves in stagnant, shaded water. 



This station was near the east edge of the smaller pond 

 where the water is quiet, more or less stagnant, and from three 

 to four inches deep. The sun shone here only for a few hours 

 in the morning; tall white poplars {Populus alba Linnaeus) 

 shaded the water for the remainder of the day. Throughout 

 October, the decaying leaves on the bottom were covered by a 

 thick green sediment. The leaves were carefully lifted and this 

 sediment allowed to drain off into a tumbler. Examination 

 showed this color to be due to enormous numbers of a small 



