60 THE MICROSCOPE AND ITS REVELATIONS. 



Microscopists are in the habit of keeping by them stocks of desiccated 

 Eotifers, which can be distributed in the condition of dry dusty powder. 

 The desiccating process has been carried yet farther with the tribe of Tar- 

 digrada ( 453, iv.); individuals of which have been kept in a vacuum 

 for thirty days, with sulphuric acid and chloride of calcium, and yet have 

 not lost their capability of revivification. These facts, taken in connec- 

 tion with the extraordinary rate of increase mentioned in the preceding 

 paragraph, remove all difficulty in accounting for the extent of the dif u- 

 sion of these animals, and for their occurrence in incalculable numbers in 

 situations where, a few days previously, none were known to exist. For 

 their entire bodies may be wafted in a dry state by the atmosphere from 

 place to place; and their return to a state of active life, after a desicca- 

 tion of unlimited duration, may take place whenever they meet with the 

 requisite conditions moisture, warmth, and food. It is probable that the 

 Ova are capable of sustaining treatment even more severe than the fully 

 developed Animals can bear; and that the race is frequently continued 

 by them when the latter have perished. It is not requisite to suppose, 

 however, that in any of the foregoing cases the desiccation is com- 

 plete; for it appears that Wheel- Animalcules, in drying, exude a glutinous 

 matter that forms a sort of impervious casing, which may keep-in the re- 

 maining fluid. 1 When acted on by heat as well as by drought, Rotifers 

 and Tardigrades lose their vitality; yet the former have survived a grad- 

 ual heating up to 200 Fahr. 



453. The principles on which the various forms that belong to this 

 Class should be systematically arranged, have not yet been satisfactorily 

 determined. By Prof. Ehrenberg, the disposition of the ciliated lobes or 

 wheel-organs, and the inclosure or non-inclosure of the body in a lorica or 

 case, were taken as the basis of his classification; but as his ideas on both 

 these points are inconsistent with the actual facts of organization, the 

 arrangement founded upon them cannot be received. Another division 

 of the class has been propounded by M. Dujardin, which is based on the 

 several modes of life of the most characteristic forms. And in a third, 

 more recently put forth by Prof. Leydig, the general configuration of the 

 body, with the presence, absence, and conformation of the foot (or tail) 

 are made to furnish the characters of the subordinate groups. Either of 

 the two latter is certainly more natural than the first, as bringing 

 together for the most part the forms which most agree in general orga- 

 nization, and separating those which differ; and we shall adopt that of 

 M. Dujardin as most suitable to our present purpose. 



I. The first group includes those that habitually live attached by the 

 foot, which is prolonged into a pedicle; and it includes two families, the 

 Floscularians and the Melicertians, the members of which are commonly 

 found attached to the stems and leaves of aquatic plants, by a long pedi- 

 cle or foot-stalk, bearing a somewhat bell-shaped body. In one of the 

 most beautiful species, the Stephanoceros Eicliornii (Fig. 312), this body 

 has five long tentacles, beset with tufts of cilia, whilst the body is inclosed 

 in a gelatinous cylindrical cell. At first sight, the tenacles of this Roti- 

 ler may seem to resemble those of the Polyzoa\ but, if there are carefully 

 illuminated, the filaments which beset them will be found to be much 

 larger, to be arranged differently, and to exhibit only an occasional 

 motion, not at all resembling the regular rhythmical vibrations of the 



1 See Davis in " Monthly Micros. Journ ," Vol. ix. (1863), p. 207; also Slack, at 

 p. 241 of same volume. 



