THE LOBOSA 79 



It may be regarded as extremely doubtful whether the forms 

 that the Amoebae present really indicate true differentiation into 

 definite species, or represent the varying influence of certain ex- 

 ternal conditions acting upon one species, or, again, represent 

 different phases in the life -history of one or more distinct 

 species. Thus it has been observed that when the amoebae 

 found on the surface of decomposing hay infusions are placed upon 

 a slide, broad lobate pseudopodia begin gradually to be extended 

 in various directions and the general form of Amoeba proteus is 

 assumed. After a time, when progression may be induced in one 

 direction, the body becomes elongated and more or less pointed at 

 the anterior end, so that the form becomes similar to that known 

 as A. Umax. If the water be made very feebly alkaline the amoebae 

 contract into a spherical shape with very short dentate pseudopodia, 

 similar to A. guttula, and then protrude long pointed pseudopodia 

 similar to those of Dactylosphaera radiosa. 1 



The forms usually attributed to the genus Ouramoeba, Leidy, 

 have been shown to be Amoebae in which fungal filaments are 

 growing (Poteat [21]). The filaments arise from spores which are 

 always situated in the neighbourhood of the contractile vacuole. It 

 has been suggested that the fungus receives nourishment from the 

 waste products of the amoeba. These filaments have been observed 

 in Amoebae attributed to the species A. villosa, A. linucleata, and 

 A. proteus. 



The life -history of no species of Amoeba has yet been fully 

 worked out, but Calkins (7) has shown that Amoeba proteus 

 normally passes through an early stage when the pseudopodia are 

 relatively long and more pointed and similar to those of A. radiosa ; 

 and Scheel (29) has proved that the uninucleate condition is 

 succeeded by a multinucleate condition previous to encystment. 



Calkins suggests that the life-cycle of Amoeba proteus may be 

 somewhat as follows : The zygote gives rise to a small radiate 

 form, which develops into the uninucleate type-form. This 

 encysts and by schizogony gives rise to uninucleate Amoebae, 

 which develop into the multinucleate type-form. The multi- 

 nucleate type-form encysts and gives rise to the gametes, which 

 conjugate to form the zygotes. 



Paramoeba, Schaudinn. Several radiating pseudopodia. A well- 

 defined chromatin body is present in the cytoplasm close to the nucleus. 

 Swarm-spores with two flagella. P. eilhardi was found in a marine 

 aquarium in Berlin. 10-90 //,. P. hominis, a human parasite (p. 83). 



Dactylosphaera, Hertwig and Lesser (Fig. 12, 1), is distinguished from 

 Amoeba by the numerous rigid pseudopodia, which do not completely 

 retract when at rest. Freshwater. Maximum 120 /z. 



1 Verworn, General Physiology, English translation, 1899, p. 184 ; and Doflein, 

 F., Archiv Prot. Suppl., 19,07, p. 250. 



