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. 1 



" How long the eggs lie on the bottom of the 

 river, and how many days elapse before the larvae 

 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 six 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 year the larvae 

 are twice as long, but three years are required .before 

 they attain their full size. 2 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. 



1 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. 



