422 MICROSCOPIC FORMS OF ANIMAL LIFE. 



the preceding. How the Aspidisca-iorm iu its turn gives origin 

 to the Oxytricha-iovva, has not yet been made out. A sexual 

 process, it may be almost certainly concluded, intervenes some- 

 where ; but other transformations may not improbably take place, 

 before the latter of these types is reproduced. 



274. A like succession of phenomena has been observed 

 among several other forms of Infusoria ; so that, considering the 

 strong general resemblance in kind and degree of organization 

 which prevails throughout the group, it does not seem unlikely 

 that the " encysting process" occurs at some stage of the life of 

 nearly all these Animalcules, just as the " still" condition alter- 

 nates with the " motile" in the most active Protophytes (§§ 152-6). 

 And it is not improbably in the " encysted" condition that their 

 dispersion takes place ; since they have been found to endure 

 desiccation in this state, although, in their ordinary condition of 

 activity, they cannot be dried up without loss of life. When 

 this circumstance is taken into account, in conjunction with the 

 extraordinary rapidity of multiplication of these Animalcules, 

 and with the fact that a succession of different forms may be 

 presented by one and the same being, the difficulty of account- 

 ing for the universality of their diffusion, which has led some 

 Naturalists to believe in their "spontaneous generation," and 

 others to regard them as isolated particles of higher organisms 

 set free in their decomposition so as to constitute an " equivocal 

 generation," is as readily got over as we have seen it to be in 

 the case of the Fungi (§ 211). Although it may be stated as a 

 general fact, that wherever decaying organic matter exists in a 

 liquid state, and is exposed to air and warmth, it speedily be- 

 comes peopled with these minute inhabitants, yet it has been 

 experimentally proved by Prof. Schultz, that perfectly free access 

 of air to such infusions, is essential to the appearance of Animal- 

 cules in them. Por having kept infusions of decaying animal 

 and vegetable matter, in air which had been filtered (so to speak) 

 of any floating germs it might contain, by passing through 

 either a red-hot tube or strong sulphuric acid, he found that no 

 Animalcules made their appearance under these circumstances, 

 even after the lapse of several weeks ; although they were seen 

 in abundance after the free exposure of the same infusions to 

 the atmosphere for a few bours only. Hence it may be fairly 

 inferred, that, as seems to be the case with the Fungi, the dried 

 cysts or the germs of Infusoria are everywhere floating about in 

 the air, ready to develope themselves wherever the appropriate 

 conditions are presented ; and all our knowledge of their history, 

 as well as the strong analogy of the Fungi, seems further to 

 justify the belief, that the same germs may develope themselves 

 into several different forms, according to the nature of the liquid 

 in which they chance to he deposited. This is a subject pe- 

 culiarly worthy of the attention of Microscopic observers ; who 

 can scarcely be better employed than in tracing out the succes- 



