GENUS AMCEBA— AMCEBA EADIOSA. 59 



which, he says, approximates ^^th mm., and has many variable processes in 

 the form of long, narrow, acute rays. Dujardin has described apparently 

 the same ci'eature as pertaining to three species with the names of A. radi- 

 osa, A. hr adnata, and A. ramosa. 



A small Amceba, of habitually radiate appearance, as usually seen, is 

 common in many situations. The radiate form, however, in a great meas- 

 ure, appears to be incidental to the animal being free and floating, for when 

 it is creeping upon surfaces it loses much of this specific character. 



AmoBba radiosa is a comparatively small inactive species, and 

 ordinarily is observed suspended in water almost motionless and with its 

 ray-like pseudopods apparently fixed as if they were rigid. It possesses 

 comparatively little irritability, and at times, when it comes into the vicinity 

 of a Stentor, a Vorticella, or a Rotifer, it may be seen whirling about in the 

 currents produced by these animals, with its form unchanged and its pseu- 

 dopods extended, as if it had no inherent power of motion. On closely 

 watching the Amoeba, as it remains quietly suspended in water, it is ob- 

 served very slowly to undergo more or less change of shape, and the 

 pseudopods are noticed gradually to contract or elongate, to bend from 

 side to side in a gentle oscillating manner, or to become twisted or bent in 

 an angular direction. Sometimes more quickly than usual, a pseudopod 

 will be withdrawn in a tortuous course. While one or two pseudopods 

 are almost imperceptibly shortened or lengthened or entirely withdrawn, 

 new ones will as slowly appear and elongate. 



In floating or swimming, Amoeba radiosa glides along almost imper- 

 ceptibly, and much in the same manner as the common Sun-animalcule. 

 Perty speaks of its locomotion as being very feeble. Dujardin says of 

 certain specimens, they lived particularly in the flocculent pellicle on the 

 surface of the water, and when detached they floated and were drawn into 

 the eddies produced by Vorticellas. Of others, described by the same 

 author under the name of Ammha hrachiata, he says they float in the water 

 when agitated; but when after a certain time they become fixed on a 

 surface, they apply themselves to it in extension more or less hke other 



AmoebaB. 



Characteristic specimens of Amoeba radiosa are to be found almost 

 everywhere, and at all times, where other Fresh-water Rhizopods occur. 



