776 MICEOSCOPIC FORMS OF ANIMAL LIFE 



consumed by the Coleps that its body is .sometimes quite altered in 

 shape by the distension. This circumstance, however, by 110 means 

 proves that such creatures possess a sense of taste and a power of 

 determinate selection ; for many instances might be cited in which 

 actions of the like apparently conscious nature are performed with- 

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

 the nature and direction of the ciliary currents, may be best studied 

 by diffusing through the water containing the animalcules 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, seems to receive 

 an investment of firm sarcodic substance, resembling the ' digestive 

 vesicles' of Noctiluca, and to be then projected into the softer 

 endosarc of the interior of the cell, its place in the oesophagus being 

 occupied by other particles subsequently ingested. (This ' moulding/ 

 however, is by no means universal, the aggregations of coloured 

 particles in the bodies of Infusoria being often destitute of any 

 regularity of form.) A succession of such pellets being thus intro- 

 duced into the cell-cavity, a kind of circulation is seen to take place 

 in its interior, those that first entered making their way out after 

 a time (first yielding up their nutritive materials), generally by a 

 distinct anal orifice, but sometimes by the mouth. 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 firm membranous in- 

 vestment. The mode of formation of food vacuoles has been carefully 

 studied by Miss Greenwood 1 in Carchesium polypinum, which may 

 be recommended for the study of the processes of protozoan 

 digestion. When the animalcule 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 protoplasm ; and their fluid sometimes shows a tinge of colour. 

 which seems to be due to the solution of some of the vegetable 

 chlorophyll upon which the animalcule may have fed last. 



Contractile vesicles (fig. 592, 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 ciliated animalcules ; 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 midistinguishable, and 

 coming into view again as they are refilled. These vesicles do not 

 change their position in the individual, and they are pretty 

 constant, both as to size and place, in different individuals of the 

 same species ; hence they are obviously quite different in character 

 from the * vacuoles.' In Paramecium there are always to be observed 

 two globular vesicles (fig. 592, B, a. a), each of them surrounded by 



1 PML Trans. 1894, B. pp. 855-83. 



