352 SALMON AND TROUT. 
of all, but, beyond this, their life-history is, as far as known, 
identical, whether in the immature larval stages when under 
the water; or the subimago rising from the surface of the 
stream and flying to the shore; or the perfect insect, the 
imago, under which form the reproductive functions are 
exercised. 
The eggs, when deposited on the surface by the female 
imago, sink to the bottom of the river, and after the lapse of a 
certain time the young May-flies are hatched out in the form of 
tiny active larve. It is probable that the comparative tem- 
perature and depth of the water, and the surrounding circum- 
stances tending to increase or diminish the quantity of light 
and sunshine, may have some effect in retarding or advancing 
the period intervening between the deposition of the eggs and 
the birth of the larve. Having succeeded in hatching the 
eggs of Ephemera danica in captivity, I am in a position to give 
some precise data, which, however, must be taken as showing 
the result only with this particular species under particular con- 
ditions of light and temperature. A number of eggs taken on 
June 9, 1887, hatched on August 15 in the same year, a period 
of sixty-seven days. 
The new-born larvee at once commence digging their way 
into the mud by means of their tusk-shaped mandibles and 
forelegs, and form tubular horizontal galleries of a diameter 
only slightly greater than that of their bodies, but, according to 
the observation of Pictet, not sufficiently large for them to be 
able to remain in these retreats while growing. As they increase 
in size they desert the galleries previously dug and form fresh 
ones ; as, however, they always affect water of a certain depth, 
in rivers subject to sudden floods they are obliged to change 
their quarters from time to time in order to preserve these con- 
ditions. 
As the larva grows it sheds its outer skin many times, some 
further development of the various organs taking place with 
each moult. The entire larval existence is passed in compara- 
tively still portions of the stream, buried in the mud at a depth 
