154 THE HAUNTS OF LIFE 



Gate, and put it in a pill-box. It lay dry for 

 forty years, but, when some of the dry dust was 

 then put into a saucer full of water, it gave rise 

 after a short time to some lively water-fleas. 

 Their resting-eggs had retained their vitality for 

 longer than an average human lifetime. This 

 explains why pools, which have been dry for 

 several years, are found teeming with little 

 creatures soon after they have been once more 

 filled with water. The power of lying low in the 

 mud also helps us to understand what we con- 

 sidered already, that similar fresh-water animals 

 often occur in widely separated basins. For 

 mud may be transported for long distances in 

 various ways, e.g. on the coats of cattle, and on 

 the feet of birds. When the caked mud is 

 dissolved off in the water, the minute animals 

 may become lively again, or sometimes it seems 

 to be their well-protected eggs that have sur- 

 vived. 



In tropical Africa there is a strange fish 

 which has lungs as well as gills. It is known 

 as the " mud-fish " because, when the water of 

 the lake in which it lives gets very low, it 

 burrows down into the mud, and works itself 

 round and round until it has formed a complete 

 mud-casing round its body. This dries and 



