154 THE HAUNTS OF LIFE 
of Gihon, at the Jaffa 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 aver- 
age 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 considered 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 survived. 
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 bur- 
rows down into the mud, and works itself 
round and round until it has formed a com- 
plete mud-casing round its body. This dries 
