62 NATURAL HISTORY. 
Among thofe that do not change their place, there are a fort of tuits 
en each fide, which fome have taken for fins ; but Mr Reaumur found by 
the help of a microfcope, that they are the gills of this infe@, which 
he affirms to be a real filh: the number of the gills is not the fame in 
different kinds, for Sqwammerdam tells us, there are fix on each fide, 
and Reaumur feven. 
While thefe infects continue in the ftate of worms, they are of a. 
flefh-colour, and the s.urelias, when they have been juft transformed, 
are the fame; but when they are ready to become flies, they turn to a 
pretty ftrong yellow, and the corflet is brown: the Ephemeras of Hol- 
fand appear about St Foha’s day, when clouds of them may be feen; 
whereas they do not appear about Paris till the middle of dugu/?. 
Some make their appearance about fix o’clock, that is about two hours 
before fun-fet, while others are not feen till the fun is juft ready to dif- 
appear. 
"Though the lives of thefe flies are fo fhort, they have fufficient time 
to perform the end of their produétion; for they are no fooner meta- 
morphofed into flies but they begin to lay their eggs, which fome do 
in rivers, and others on any fubftance that they meet with; and they 
are faid to lay more at a time than any other infe@ whatever; for each 
bunch of eggs is faid to confift of three hundred and fifty, and there 
are generally two bunches. 
There are feveral forts of flies, belonging to this clafs, that live fe- 
weral days, as was before obferved; one kind of which are in a condi- 
tion different from all other flies, for they have ftill another cafe or 
fkin to get rid of: thefe are to be feen in the fields, and in woods dif- 
tant from any water; buit it is more common to find them among © 
thofe that are neareft. Some of thefe may be feen flicking upon walls 
and trees, and often with the head downwards, without changing place, 
or having any fenfible motion; for they wait for the moment when 
they fhall be divefted of their laf{ incommodious garment ; but fome- 
times this does not happen till twenty-four hours are expired. 
Linnaeus places them among flies that have nervous wings, and takes 
notice of fix different forts. ‘The firft kind of Ephemera has wings 
fpotted with brown, the tail confifting of three threads; and this is 
found near lakes. 
2. The fecond has white wings that are ftreaked, and has a forked 
tail. It is called in the tranfa@ions of Up/al, the Ephemera with wings 
of a whitifh fefh-colour; they are feen fluttering in fwarms by the fides 
of waters. 
3. The Ephemera with white ftreaked wings, may be diftinguifhed 
from all others of this kind, by that mark only. 
4 The brown £phemera with a tail confifting of two threads, with - 
white wings. 
5. The Ephemera with white wings, having a thick blackifh edges 
and a tail confifting of two threads. It is called in the Up/al traniac- 
tions, the leaft Ephemera with white wings. 
6. The black Ephemera with white lower wings. 
The Ephemera with white reticulated wings, and two hairs at the tail, 
is a pretty large flic, with an oblong flender whitifh body, except to- 
wards the tail, where it is brown: the head is fmall, and on its top 
there are two prominences, which have the appearance of eyes, “= 
f, ar 
