340 



THE AMERICAN NATURALIST [Vol. LIV 



IOx eyepieces and the 4 mm. objective were found great 

 enough for the majority of the forms. 



In the following descriptions of the genera and species 

 the attempt has been made to indicate the characters 

 which are the most prominent ones of the members of 

 each group, those by which the identification can usually 

 be made. Hitherto less attention than the subject seems 

 to deserve has been given to the manner in which these 

 lower forms make their way through the water— to what 

 may be called their natatory habits. Many forms show 

 natatory habits which seem to be of a constancy and a 

 distinctness sufficient to warrant their use as character- 

 istics for identification. This feature has been given at- 

 tention in the following descriptions because it has been 

 found a helpful one in identifying the forms. 



It is here suggested that the vibratory motions which 

 some of the smaller flagellates, like Pleuromonas and 

 Elvirea, exhibit, may be due in part to the influence of 

 pedesis, or Brownian movements. Carpenter states 5 

 that all particles suspended in water below 3 /soo of an 

 inch (49 microns) exhibits this phenomenon, and it is a 

 matter of observation that the smaller the particle the 

 more pronounced the vibration. 



ORDER MONADIDA 



Genus Mastigamoeba Schultze. 



Body amoeboid, changing shape slowly as pseudopodia 

 are protruded, usually from the sides or posterior por- 

 tion of the body. Flagellum long, fine, and not easily 

 seen at first in its entirety, because of its rapid motion. 

 These forms move with either a true amoeboid motion, or 

 swim by means of the flagellum. Conn states that in 

 swimming the pseudopodia are retracted, yet we have 

 noticed frequent exceptions in both species. The swim- 

 ming of these species is clumsy, due perhaps to the ir- 

 regularity of the body. 



s"The Microscope and Tts Revelation?." 



