Feb., 1920] The Protozoa of Mirror Lake 97 



Station H occupied a position near the east shore of the bay 

 in the east end of the larger pond. The water here was quiet, 

 about three inches deep and was shaded during only a few hours 

 in the morning. Passing by this part of Mirror Lake, my 

 attention was attracted by a mass of bright yellow flocculent 

 material which covered the bottom. My interest was aroused 

 to know what it was and what Protozoa were present in 

 it. Some of the material was lifted into a tumbler with a 

 spoon. Examination showed it to consist of dead filaments 

 of the alga Oedogo?iium. This remained abundant as long as 

 the temperature of the water stayed below five degrees centi- 

 grade; when it became warmer than that, the living green alga 

 had resumed its growth. The flagellates which predominated 

 were Euglena viridis, Peridiniuni tahidatiim and Synura uvella. 

 Lembadion bidlinum, a ciliate, was plentiful and was taken 

 exclusively at this station. Pleuronema chrysalis found an ideal 

 habitat among this decaying material. 



STATIONS I AND l'. 



Algae covering submerged wooden posts, on different sides of 

 the pond, but both well exposed to light. 



Two submerged wooden posts on opposite sides of the larger 

 pond, but apparently showing similar conditions, were selected 

 for these stations. The sun shone on both of them throughout 

 the day and the temperatiire of the water was the same in both 

 places. A thick growth of algae (mostly Oedogonium) covered 

 the posts below the surface of the water. This was scraped off 

 and the two collections each time were compared with each 

 other. It was interesting to note that approximately the same 

 Protozoa were found in both places at the same times, despite 

 the distance between the stations. The heliozoan Raphi- 

 diophrys viridis was abundant in November. Holosticha vernalis, 

 Stentor roeselii, Frontonia sp.? and Euglena sp.? were common 

 at these places throughout the period of study. 



STATION J. 



Algae and sediment in clear, fresh spring water, well exposed 

 to light. 



Station J was located just north of the east end of the larger 

 pond, in the cement bowl into which the spring bubbles. The 



