INFUSORIA, THEIR MODE OF APPROPRIATING FOOD. 417 



selection ; for many instances might be cited, in which actions 

 of the like apparently conscious nature are performed without 

 any such guidance. The ordinary process of feeding, as well as 

 the nature and direction of the ciliaiy currents, may be best 

 studied by diffusing through the water containing the Animal- 

 cules, a few particles of indigo or carmine. These may be seen 

 to be carried by the ciliary vortex into the mouth, and their 

 passage may be traced for a little distance down a short (usually 

 ciliated) oesophagus. There they commonly become aggregated 

 together, so as to form a little pellet of nearly globular form ; 

 and this, when it has attained the size of the hollow within 

 which it is moulded, is projected into the " general cavity of the 

 body," where it lies in a vacuole of the sarcode, its place in the 

 oesophagus being occupied by other particles subsequently 

 ingested. This " moulding," however, is by no means universal ; 

 the aggregation's of colored particles in the bodies of these 

 animals being often destitute of any regularity of form. One 

 after another of such particles being thus introduced into the 

 interior of the body, each aggregation seems to push on its pre- 

 decessors; and a kind of circulation is thus occasioned in the 

 contents of the cavity. The pellets that first entered make their 

 way out after a time (after yielding up their nutritive materials), 

 generally by a distinct anal orifice, sometimes, however, by any 

 part of the surface indiflsrently, and sometimes by the mouth. 

 A circumstance which seems clearly to indicate that they cannot 

 be enclosed (as Prof. Ehrenberg maintains) in distinct stomachal 

 cavities, is that, when the pellets are thus moving round the 

 body of the Animalcule, two of them sometimes appear to 

 become fused together, so that they obviously cannot have been 

 separated by any membranous investment. When the Animal- 

 cule has not taken food for some time, "vacuoles" or clear 

 spaces, extremely variable both in size and number, filled only 

 with a very transparent fluid, are often seen in its sarcode ; their 

 fluid sometimes shows a tinge of color, and this seems to be due 

 to the solution of some of the vegetable chlorophyll upon which 

 they may have fed last. 



270. Contractile vesicles (Figs. 194, 195, a, a), usually about 

 the size of the "vacuoles," are found, either singly or to the 

 number of from two to sixteen, in the bodies of most Animal- 

 cules ; and may be seen to execute rhythmical movements of 

 contraction and dilatation at tolerably regular intervals, being so 

 completely obliterated when emptied of their contents, as to be 

 quite indistinguishable, and coming into view again as_ they are 

 refllled. These vesicles do not change their position in the in- 

 dividual, and they are pretty constant, both as to size and place, 

 in different individuals of the same species ; hence they are ob- 

 viously quite different in character from the "vacuoles." "What 

 is their purpose in the economy of these creatures can be^ only 

 vaguely guessed at; it may be surmised to be the diflusion 



27 



