288 NATURAL HISTORY OF AQUATIC INSECTS CH. 



they are rounded discs, which sink at different rates ; 

 hence if a number of the eggs are gently lowered 

 into the water on the point of a knife, they are 

 seen to spread as they descend.^ 



" How long the eggs lie on the bottom of the 

 river, and how many days elapse before the larva; 

 emerge, is known only to God. Something might be 

 made out upon these points if any one would search 

 the bottom of the stream at frequent intervals, or 

 keep the eggs in a basin with water and mud. 



" Some time after the descent of the eggs, a crowd 

 of minute worms, each with si.x legs, makes its ap- 

 pearance. These do not differ in shape from the 

 older larvae. Their growth is so slow that after a 

 year, viz., in the following June, they are only a third 

 of the length of the larvae then ready to enter the 

 winged state. At the end of another }'ear the larvae 

 are twice as long, but three }'ears are required before 

 they attain their full size.- Not only do these larvae 

 of different ages differ in size, but also in the degree 

 of development of the wings. The small larvae, a 

 year old, exhibit no trace of wings ; after two years 

 the wings are visible, and enclosed in special sheaths ; 

 at the end of the third year they are quite plain and 

 ready to burst forth. 



' If a handful of ivory counters are thrown into deep water, 

 some descend edgewise, and reach the bottom long before 

 others, which happen to take a horizontal position. Some such 

 difference of position and not of specific gravity, seems to be 

 referred to by our author. 



« 2 Confirmation of this is desirable. Some Ephemeras spend 

 one, and some two years as larvae, but no other case of an 

 Ephemera remaining a larva for three years is on record. 



