328 



PROTOZOOLOGY 



few, digitate, simple or branched; 2 nuclei; several contractile 

 vacuoles; fresh water. Numerous species. 



A. vulgaris E. (Fig. 150, a, h). Height of test about 1/2 the 

 diameter; dome of hemispherical test evenly convex; aperture 

 circular, central; colorless, yellow, or brown; protoplasmic body 

 conforms with the shape of, but does not fill, the test; lobopodia 

 hyaline; 2 vesicular nuclei; several contractile vacuoles; test 30- 

 lOO/i in diameter; in the ooze and vegetation in stagnant water 



Fig. 150. a, b, Arcella vulgaris, Xl70; X230 (Leidy); c, A. discoides, 

 X170 (Leidy); d, A. mitrata, Xl40 (Leidy); e, f, A. catinus. Xl70 

 (Cash); g-i, .4. dentata, Xl70 (Leidy); j, k, ^4. artocrea, Xl70 (Leidy). 



and also in soil. Of several varieties, two may here be mentioned : 

 var. angulosa (Perty), test smaller, 30-40At in diameter, faceted, 

 forming a 5- to 8-sided figure, with obtuse angles; var. gihhosa 

 (Penard), test gibbous, surface pitted with circular depressions of 

 vmiform dimensions; 45-50yu up to lOO^i in diameter. 



A. discoides E. (Fig. 150, c). Test circular in front view, plano- 

 convex in profile; diameter about 3-4 times the height; test color- 

 ation and body structure similar to those of A. vulgaris; test 70- 

 260 fj, in diameter; in fresh water. 



A. mitrata Leidy (Fig. 150, d). Test balloon-shaped or poly- 

 hedral; height exceeds diameter of base; aperture circular, crenu- 



