106 POND LIFE. 



substances which are most easily washed away from the hills. 

 If these be of red sandstone, you may expect to find a red sandy 

 bottom to the pond ; if the hills be of blue or of grey clay, the 

 bottom of the pond will consist of a similar clayey mud. 



Now we may attack the question, how did life get into ponds ? 

 There must have been a time when there was a pond without 

 anything living in it. It is not my intention to tell you how living 

 things came to be in the first instance ; that is a question upon 

 which we can only speculate. We have no knowledge about it. 

 But we may assume that there is plenty of life in the world, and 

 that there is a pond left to itself, and we can try to ascertain how 

 it would become stocked with living animals and plants. In the 

 first instance, the air is not pure, even in the country, but is full of 

 dust of all kinds, amongst which a very careful examination 

 reveals living organisms. Many different kinds of these germs are 

 to be found in the atmosphere, so that the very fact of rain falling 

 through the atmosphere into a pond, will bring living things 

 into it. But these are exceedingly small, and if our pond 

 depended simply upon them we should not have any of the higher 

 forms of life in it. ^ ou will have noticed that many plants have 

 exceedingly small seeds, so small indeed that they can be carried 

 about by the wind ; some of these might reach the pond. Again, 

 many seeds are eaten by birds, and thus carried away and dropped 

 in various places, and often in ponds or on their banks. Animals, 

 too, can be carried in a similar manner. There are instances of 

 birds caught at sea, far from land, which, when examined, have 

 been found to have small snails, frog-spawn, and other similar 

 matters sticking to their legs. So that it is easy to see how by 

 these means many animals could be transferred from one pond to 

 another. These facts are interesting, not principally as regards our 

 pond, but most especially when we come to consider similar 

 questions in relation to islands which are situated far out in the 

 ocean, and to find out how they have been stocked with plants 

 and animals. 



The fact of plants and animals living in the water has 

 a great influence upon their structure, and modifies them in 

 many ways, so that those which live in the water are, in general, 

 fitted to live nowhere else. Not many animals, and still fewer 

 plants, can live both on land and in water. 



