50 HISTORY OF BRITISH ZOOPHYTHES. 
ment for the insect race. Plants are covered with aphides, 
greedily sucking their juices, and constantly, as it would 
seem, in the act of sucking. It cannot be doubted but 
that this is a state of gratification. What else should fix 
them so close to the operation, and so long? Other species 
are running about, with an alacrity in their motions which 
carries with it every mark of pleasure. Large patches of 
ground are sometimes half-covered with these brisk and 
sprightly natures. If we look to what the waters produce, 
shoals of the fry of fish frequent the margins of rivers, of 
lakes, and of the sea itself. These are so happy that they 
know not what to do with themselves. Their attitudes, 
their vivacity, their leaps out of the water, their frolics in it 
(which I have noticed a thousand times with equal attention 
and amusement), all conduce to show their excess of spirits, 
and are simply the effects of that excess. Walking by the 
sea-side in a calm evening, upon a sandy shore, and with 
an ebbing tide, I have frequently remarked the appearance 
of a dark cloud, or rather very thick mist, hanging over the 
edge of the water, to the height perhaps of half a yard, and 
of the breadth of two or three yards, stretching along the 
coast as far as the eye can reach, and always retiring with 
the water. When this cloud came to be examined, it proved 
