756 THE AMERICAN NATURALIST [Vol. XLIX 



These pools are large and one or two feet deep and have 

 thin mud overlying rock bottom. Both lie near Fall 

 Creek. 



The pools (K, x, x 1 , x s , x*) near Cascadilla Creek pre- 

 sented the only specimens of Dinobryon that were seen. 

 These pools are permanent and deep and have stony 

 bottom. 



It may be significant that in the low-ground pools there 

 were few kinds of diatoms and in only one such pool (A) 

 were there any desmids. 



The Animal Population.— The floating and entangled 

 vegetation of these masses supports a large animal popu- 

 lation. The protozoans found were particularly varied 

 and interesting. Ameba, Arcella and Difflugia appeared 

 irregularly in the upland pools. Cochlio podium and Mas- 

 tigameba were rare. No other Rhizopods were observed. 

 The ciliates were not determined before March, with the 

 exception of Paramecium, which was listed from the first. 

 In the twenty collections made since March first, fifteen 

 genera of ciliates have been observed. Paramecium was 

 constant and abundant. Among the larger representa- 

 tives of the group, Coleps, Chilodon, Colpidium, Stylo- 

 nychia and Vorticella appeared frequently and in large 

 numbers. Stentor, Dipleurostyla and Amphileptus were 

 less frequent, as were the smaller members of the group, 

 namely, Euplotes, Halteria and Askanasia. Coleps was 

 especially noticeable in pool y 1 , while Vorticella was plen- 

 tiful in pools D and G. Pools D, G and J, which supplied 

 the largest number of genera and of individual ciliates, 

 are shallow ditch-pools with muddy bottom, while A and 

 Y in which smaller numbers were found, but still many 

 genera, are larger and deeper, but have muddy bottom or 

 muddy water. From this it seems evident that these 

 protozoa prefer water with inorganic material in suspen- 

 sion, although they are said to avoid water polluted by de- 

 caying organic matter. These tiny creatures forage bus- 

 ily among the algal filaments, some swimming and rotat- 

 ing smoothly, others, such as Halteria and Stylonychia, 



