^o. 603] 



ECOLOGY OF THE PROTOZOA 



167 



ing feature, but the position of the buccal cavity is virtu- 

 ally constant. 



Euglena deses (Fig. 15) is recognizable by its enor- 

 mously elongated body, for the propulsion of which its 

 small flagellum seems inadequate. It frequently assumes 

 an almost amoeboid form, and not infrequently contracts 

 to such an extent as to become nearly globular. Being 

 variable in size, its form, when swimming by means of its 

 flagellum, offers the readiest means of identification. 



One particular locality, given especial notice, deserves 

 detailed mention. This was a spring pool in a boggy up- 

 land meadow, almost hidden among large tufted clumps 

 of luxuriant sedge-like grasses. The depth of the pool 

 was about four inches, and its area about six square feet. 

 Although exposed to the rays of the sun during the greater 

 part of the day, yet the temperature of the water was kept 

 low by a constant trickle of cold water from seepage 

 springs in the glacial clays which underlay several acres 

 of the region. The iron content of the water was unusu- 

 ally high, though the pool was crystal clear. Of higher 

 aquatic plants there were none ; Desmids were numerous ; 

 Diatoms were sufficient in numbers to form a brown film 

 over the entire bottom. The pool contained seven large 

 black-nosed dace, and other adjacent pools harbored sev- 

 eral more. Snails, Limnea and Physa crawled every- 

 where. With the exception of half a dozen large Hydro- 

 philidcB there were no aquatic insects, and but very few 

 E^itomostraca. 



The predominant forms were Monas fiuida and irregu- 

 laris, occurring not alone in the bottom film but every- 

 where throughout the water and in great numbers. One 

 species of Holophrya and Cercomonas crassicauda (but 

 few individuals of each) completed the census of the 

 forms. 



En\^ronmental Type No. IV : Clear Small Pools with 

 Abundant Decomposing Organic Sediment 

 Small clear pools in depressions in rocks containing de- 

 caying leaf material and a small quantity of such algae as 



