208 GENERAL HISTORY OF THE INFUSORIA, 



animals have no definite aperture for food — no mouth. This absence of a 

 mouth, on anatomical grounds alone, involves that of an alimentaiy canal, or 

 of a polygastric structure such as Ehrcnberg imagined. The digestive cells, 

 so called, of Arcellina are nothing more than hollow spaces or vacuoles (XXII. 

 7, 8, 9), which spontaneously and irregularly develope themselves in the mu- 

 cous sarcode substance. They especially make their appearance after the in- 

 troduction of food, the particles of which generally appear enclosed within 

 them, and to be surrounded by a fluid. In the allied organisms represented 

 by Actinophrys, M. Claparede states that the particle of food always hes in a 

 cavity filled with fluid — a vacuole, — and that the fluid is of a pale reddish 

 colour, with difterent refractive powers to those of water, and is in all proba- 

 bility a solvent or digestive fluid. This pale-red or reddish-yeUow tint of 

 the vacuoles is remarked also in Amoehoi ; and the observed dissolution and 

 eventual disappearance of organic matters absorbed is a sufficient proof of 

 the presence of a digestive secretion. In an Arcella vulgaris, Perty witnessed 

 the successive appearance of four vacuoles, each in its tiu^n enlarging from a 

 small roimd to a large reniform space, and thereby expanding the dimensions 

 of the animal itself. He believed them to be filled with air, and, like the 

 air-bladders of fish, to serve to float and tm^n the animals in the water, when 

 free and without solid objects to crawl upon. 



Ehrenberg states that in some Arcellina, where " digestive sacs " were 

 otherwise invisible, they were brought into view by feeding the animals with 

 coloured substances. He thus presumed on the prior existence of these cells, 

 supposing the colouring particles to be merely the means of bringing them 

 into view. The true explanation, however, is, no doubt, that the con- 

 struction of vacuoles is consequent on the introduction of food, and de- 

 pendent on the manner in which the animal substance enfolds the solid par- 

 ticles which it has seized. Obsei-vation, indeed, proves that the vacuoles 

 have no constant and definite existence and position ; for they coUapse and 

 disappear when the contents are removed or are reduced to a few fine 

 granules dispersable in the common mass. They also constantly shift their 

 position, and not unfrequently make their way to the siuface, at which they 

 bluest and disappear. As Dujardin also remarks, they sometimes form at or 

 near the surface, and may even serve as a medium for introducing foreign 

 matters into the body. 



Dr. Bailey, in his description of a new species which he names pampTiagus, 

 represents it as having (although a shell-less Rhizopod) a mouth from which 

 alone pseudopodes protrude, and a single stomach ; hence, he adds, it cannot 

 be considered po7^(7asfr?c. However, no evidence is adduced to support this 

 notion of a gastric cavity ; on the contrary, indeed, the details given stand 

 opposed to such an hypothesis, — for instance, to quote only one, that of their 

 being frequently seen transfixed by dehcate fibres of foreign matters, and 

 moving unharmed up and down them. 



Schultze states that in Foraminifera veiy clear vesicles are uniformly 

 diffused throughout the body, some entirely homogeneous, others finely 

 granular, or filled mth corpuscles. However, nuclear corpuscles, which can 

 be regarded as cells in the ordinary signification, are never found. This 

 naturalist, moreover, indicates the existence of a larger species of vesicles in 

 Gromia oviformis (XXI. 16), containing other clear corpuscles, sometimes to 

 the number of eighteen, but never strung together ; he believes Kkewise that 

 similar vesicles exist among other Fora^nimfera, and seems disposed to attri- 

 bute to them a nuclear character. 



Ehrenberg professed to discover in the Polytlialamia, in each chamber, 

 saving the last, an alimentary tube, having a greyish-green colour and very 



