AMOEBINA. 901 



granules of Plakopus, the violet granules of Amphizonella violacea, or 

 vacuoles of Zonomyxa, the oil-globule, amber or red in colour, of Diplo- 

 phrys, or the chlorophyl bodies of some species of Difflugia, Hyalosphenia 

 papilio, Heleopera picta, Arcella artocrea, Ditrema flavum, Amphitrema 

 Wrightianum' 1 . Other solid elements are fatty granules, glycogen, and, 

 when chlorophyl is present, starch (?), concretions rounded or crystalline in 

 many Amoebae, probably of an excretory character, mud or sand taken up 

 by Amoebae with fluid protoplasm and by Pelomyxa, elliptical siliceous 

 bodies secreted by the organism in Amoeba granulosa, together with food 

 or its faecal residue. The food, which is either ingested by the pseudo- 

 podia, or by the flowing round it of the protoplasm, consists of Diatoms, 

 algae, dead portions of plants, or minute animals ; it is sometimes inclosed 

 in a vacuole, sometimes in direct contact with the protoplasm 2 . The 

 latter may be expelled, sometimes inclosed in a vacuole, at any point, but 

 frequently at the posterior end of the moving body in Nuda, or at the 

 mouth of the test in Testacea. Some Amoebae, Arcella and Difflugia 

 proteiformis possess the power of evolving and reabsorbing at will in the 

 protoplasm bubbles of a gas, apparently Carbon dioxide, by means of 

 which they float to the surface of the waters they inhabit. Non-contractile 

 vacuoles are present in numbers in some Amoebae, in Pelomyxa, &c. 

 Occasionally they have been observed to disappear slowly, others ap- 

 pearing at another spot as in Zonomyxa. Contractile vacuoles may 

 be entirely absent, as in Pelomyxa and some others. Their number when 

 present is liable to variation. Amoebae very generally have 1-3 ; many 

 Testacea a single large one ; others several, in the posterior part of the 

 body, which travel to the mouth of the test to burst. Arcella may have as 

 many as twelve in a ring round the body. 



The nucleus is vesicular, i. e. provided with a membrane, nuclear fluid 

 and chromatin. The modes in which the chromatin is arranged are very 

 various, and in Amoebae, at any rate, have been asserted to characterise 

 the species (Gruber). As to number, some Nuda and many Testacea are 



1 The old question recurs, do these chlorophyl bodies belong to the organism, or are they 

 symbiotic algae? Difflugia pyriform is and D. lobostoma are both stated by Leidy to be sometimes 

 colourless, and other species of Difflugia may be occasionally green-coloured. The other five species 

 named in the text are always green. When encystation takes place, the chlorophyl granules are in- 

 cluded in the encysted mass. But attention may be drawn to fig. 12, PI. xxi, and figs. 8, 10, PI. 

 xxvi, of Leidy's monograph, where Hyalosphenia and Heleopera are respectively shown with tests 

 empty save of scattered chlorophyl bodies. Two explanations only of this fact are possible, 

 (i) that the chlorophyl bodies simply persist for a time after death, (2) that they are algae surviving 

 as symbiotic algae do after the death of their host. The small size of the bodies in question forbids 

 the supposition that they represent the contents of a cyst segmented. It may be noted that some 

 Nuda have a great propensity to ingest green algae in quantity, e. g. the Amoeba binucleata of 

 Gruber, Zoncmyxa before its encystation. 



2 Difflugia pyriformis perforates and sucks out by means of its pseudopodia the cells of 

 Spirogyra; Stokes, Amer. Monthly Micr. Journal, iii. 1882, p. 93. So, too, a naked form (? Amoe- 

 bine) described by Maupas, A. Z. Expt. ix. 1881, p. 358, and C. R. 89, 1879, p. 252. 



