432 



MICROSCOPIC FORMS OF ANIMAL LIFE. 



FTG. 20*2. 



malcule, are remarkable for their tenacity of life, even when re- 

 duced to the state of most complete dryness ; for they can be 

 kept in this condition for any length of time, and will yet revive 

 very speedily upon being moistened. Experiments have been 

 carried still farther with the allied tribe of Tardigrades ; indi- 

 viduals of which have been kept in a vacuum for thirty days, 

 with sulphuric acid and chloride of calcium (thus suffering the 

 most complete desiccation that the Chemist can effect), and yet 

 have not lost their capability of revivification. This fact, taken 

 in connection with the extraordinary rate of increase mentioned 

 in the preceding paragraph, removes all difficulty in accounting 

 for the extent of the diffusion of these animals, and for their oc- 

 currence 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 desiccation 

 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 treat- 

 ment even more severe than 

 the fully developed animals 

 can bear ; and that the race is 

 frequently continued by them, 

 when the latter have perished. 

 281. The principles on 

 which the various forms that 

 belong to this class should be 

 systematically arranged, have 

 not yet been satisfactorily de- 

 termined. By Prof. Ehren- 

 berg, the disposition of the 

 ciliated lobes or wheel- organs, 

 and the enclosure or non-en- 

 closure 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 ar- 

 rangement founded upon 

 them cannot be received. 

 Another division of the class 

 has been propounded by M. 



ste han os Eichvrnii Dujardm, 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, 



