MICROSCOPIC FORMS OF ANIMAL LIFE. 45 



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) oasophagus. 

 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 

 ( 428), 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 uni- 

 versal; the aggregations of colored particles in the bodies of Infusoria 

 being often destitute of any regularity of form. ) A succession of such 

 pellets Demg thus introduced 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 some- 

 times appear to become fused together, so that they obviously cannot have 

 been separated by any firm membranous investment. 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 sarcode; and their fluid sometimes shows a 

 tinge of color, which seems to be due to the solution of some of the vege- 

 table chlorophyll upon which the Animalcule may have fed last. 



439. Contractile Vesicles (Fig. 304, 0, 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 undistinguishable, and coming into view again as 

 they are refilled. These vesicles do not change their position in the indi- 

 vidual, and they are pretty constant, both as to size and place, in differ- 

 ent 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. 304, B, a, ), each of 

 them surrounded by several elongated cavities, arranged in a radiating 

 manner, so as to give to the whole somewhat of a star-like aspect (Plate 

 xiv., fig. 1, v, v); and the liquid contents are seen to be propelled from 

 the former into the latter, and vice versa. Further, in Stentor, a com- 

 plicated network of canals, apparently in connection with the contractile 

 vesicles, has been detected in the substance of the 'ectosarc;' and traces 

 of this may be observed in other Infusoria. In some of the larger Ani- 

 malcules, it may be distinctly seen that the contractile vesicles have 

 permanent valvular orifices opening outwards, and that an expulsion of 

 fluid from the body into the water around it is effected by their contrac- 

 tion. Hence it appears likely that their function is of a respiratory 

 nature; and that they serve, like the gill-openings of Fishes, for the 

 expulsion of water which has been taken in by the mouth, and which has 

 traversed the interior of the body. (See 399.) 



440. Of the Reproduction of the Ciliated Infusoria, our knowledge is 

 still very imperfect; for although various modes of multiplication have 

 been observed among them, it still remains doubtful whether any process 

 takes place, that can be regarded like the conjugation of the Monadina 



