98 Marvels of Pond-Life. 



of the Batracliian reptiles ; and in summer, when they 

 afford both shade and sunshine to their numerous 

 inhabitants. Small beetles, water-spiders, larvse of 

 gnats_, and other insects, rotifers, including the tubi- 

 colar sorts, and several varieties of infusoria may be 

 expected and generally found. There is, however, a 

 curious fact about ponds, big and little, which Prit- 

 chard remarks upon in his ' Infusoria,' and which 

 corresponds with our own experience, that those which 

 have proved to be well stocked with any particular 

 creature during one year, will very likely contain none 

 of it in the next. There are of course exceptions to 

 this rule, but we have often been astonished and dis- 

 appointed at finding the complete change, both in 

 populousness and population, that a revolution of 

 twelve months will make ; and it would be extremely 

 interesting to notice the changes that took place during 

 a term of years. 



Such researches might unfold some unexpected laws 

 in the succession of infusorial life. Those germs which 

 are most widely diffused, will be the most likely to be 

 developed in any mass of convenient water; but how 

 and why the rarer forms come and go is very imper- 

 fectly understood. Slight modifications in surrounding 

 circumstances will materially affect the result. Thus, 

 if we bring home a handful of conferva, and a few 

 water-plants of higher organisation, such as duck-weed 

 and anacharis, and place the whole in a glass jar full 

 of pond- water, we shall at first have a good stock of 

 objects ; but they will usually grow less and less, until 

 scarcely anything is left. If, however, we introduce a 



