i 7 6 



ROTIFERA. 



a single Rotifer thus producing in ten days forty eggs, developed 

 with the rapidity thus stated : this 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 millions, 

 and so on. Well may our ponds and ditches swarm 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 large collections 

 of fresh water ; they are met with in cart-ruts, in gutters, in rain- 

 spouts, and in the depressions 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 presence. The 

 sand in such places sometimes contains millions of them, dried 

 to dust of 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 redivivs, has derived its name from this circumstance. 

 Specimens have been kept in a dry state for four years, and then 

 resuscitated on being moistened. From this fact it becomes easy 

 to explain how collections of water, however free from such in- 

 habitants at first, become filled to swarming with Infusory and 

 Rotiferous forms of life. When the once thickly-tenanted pool, 

 says Professor Owen, is dried 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, 

 perhaps, their share of the particles which we see flickering in 

 the sunbeam, ready to fall into any collection of water, beaten 



