lO DAVENPORT ACADEMY OF SCIENCES. 



isolated form, seldom being found in aggregated quantities. The 

 common habitat is pond water in the ooze on submerged leaves, 

 sticks, etc., but the species is sometimes found in fresh water 

 among algae and diatoms. 



Usually a single nucleus is present, but often more than one 

 contractile vesicle; neither nucleus nor vesicles are, however, 

 constant in position due to the streaming movements of proto- 

 plasm. Reproduction takes place by simple cell division. 



In size the individuals vary greatly. Many observed in this 

 state have reached a length of 250 microns while other workers 

 have reported individuals of much larger dimensions. 



Amceba radiosa Ehr. 



Body a spherical mass from which radiate two or more long, 

 slender, pointed pseudopodia. (Fig. 3, PI. I.) 



If the species previously described is characterized by activity, 

 Amceba radiosa should be characterized by inactivity. Stellate 

 in its general appearance, the organism usually rests motionless 

 in the water with its ray-like pseudopodia as rigid as though it 

 possessed no power of contractibility whatever. If patient in 

 observation, however, one may occasionally see a pseudopodium 

 slowly contract and a new one extend itself from the body. 



The rays may reach a length twice the diameter of the body, 

 are flexible and may be bent from side to side without causing 

 them to be withdrawn. 



A peculiar movement of the organism has been observed to 

 take place. After resting motionless for some time the form may 

 turn itself over in the water and suddenly spring backward as 

 though under the impulse of some violent stimulus. The cause 

 for such behavior has not been determined. 



The distribution and habitat of Amceba radiosa is very similar 

 to that of Amaba proteus . In size, this species is the smallest of 

 the genus and exceedingly variable. The diameter of the body 

 of some individuals observed in this state has reached 45 microns. 



Amceba villosa Wallich. 



Body, when active, palmate in shape, usually differentiated into 

 a broad anterior and narrow posterior region, the latter produced 

 into a rounded knob-like area, the surface of which presents a vil- 

 lous appearance. (Fig. 2, PI. I.) 



