ROTIFERA. 233 



rate, raised to the tenth power, gives one million of 

 individuals derived from one parent, on the eleventh 

 day four millions, on the twelfth day sixteen mil- 

 lions, and so on. AVell may our ponds and ditches 

 sw^arm with their multitudes, and countless creatures 

 dependent on such a supply, rejoice at the abundance 

 of food thus supplied to them. 



But the Rotifera are not only thus numerous in 

 lai'ge collections of fresh water ; they are met with in 

 ca,rt-ruts, in gutters, in rain-spouts, and in the de- 

 pressions and corners of leads on the roofs of houses. 

 The fact that the water in these situations is fre- 

 quently dried up, does not at all prevent their pre- 

 sence. The sand in such places, sometimes contains 

 millions of them, dried to dust of a reddish brown 

 hue ; and if a little of this dust be put into clear 

 water, they will in a short time revive, and swim 

 about as actively as if they had never been dried. 

 One species, the Rotifer redivivus, has derived its 

 name from this circumstance. Specimens have been 

 kept in a dry state for four years, and then resus- 

 citated on being moistened. From this fact it be- 

 comes easy to explain how collections of water, how- 

 ever free from such inhabitants at first, become filled 

 to swarming with Infusory and Hotiferous forms of 

 life. When the once thickly-tenanted pool, says 

 Professor Owen, is cbied up, the inconceivably 

 minute ova, and equally imperceptible dried bodies 

 of these creatures, will be raised as dust by the first 

 puff of wind, and diffused through the atmosphere ; 

 there they may long remain suspended, forming, 

 ]:)erhaps, their share of the particles which we see 

 flickering in the sunbeam, ready to fall into any 

 collection of water, beaten down by every summer 

 shower and, by virtue of their tenacity of vitality, 

 ready to start to life wherever they may find the 

 requisite conditions for their existence. 



It is almost impossible to conceive of the out- 

 burst of fresh life caused by the return of moisture 

 in tropical climates. Immediately prior to the 



