Difcoveries made by the Microfcope, 305 
Hours may be fuppofed, from the Num¬ 
ber and fwift Succeffion of Ideas fuited to all 
thefe Purpofes, to live as long, according to 
* Swammerdam has publifhed, in Low Dutch, a curious 
Account of" what he calls the Ephemercn ; a Fly which, he 
tells us, lives but five Hours. This Infeft is found trbout all 
the Mouths of the Rhine ; and, according to his Drawings 
and Defcriptions, feems to be a Species fomawhat between 
our May-Fly (bred from the Cadew Worm) and the Libella or 
Dragon-Fly. It has four Wings, two whereof are fhorter than 
the other ; a Pair of fmall Horns, fix Legs, and two very long 
ilraight Hairs ifTuing from the Tail. Tney are feen, he fays, 
flying near the Surface of the Water, about Midfummer, for 
three fucceeding Days, but no longer in one Seafon. They 
eat nothing ; and their only Bofinefs is to generate, and drop 
their Eggs upon the Water : which Eggs , finking to the Bot¬ 
tom, produce a Kind of Worms or Maggots, that foon hollow 
themfelves Cavities in the Clay, where they abide three 
Years; growing each Year about an Inch in Length. When 
the Worm is come to its full Growth, it rifes to the Surface, 
about fix o’Clock in an Evening ; lays its Eggs, and dies 
about ten o’Clock the fame Night. 
1 am furprized that Swammerdam fhould fay, the Life 
of this Creature is no more than five Hours, when his own 
Account plainly proves that it really lives three Years : for 
it is certainly as much alive in the Worm State, as when af¬ 
terwards it becomes a Fly.-—Truth fhould be every Body’s 
Purfuit ; and for the Sake thereof I have endeavoured to clear 
up the general Miftake as to this Fly, which is frequently 
produced, upon Swammerdam’s Authority, as the moil 
remarkable Inftance we know of the Shortnefs of Lire.—But 
tho’ this Infedl happens to live much longer than was ima¬ 
gined, I make no Doubt, there are fame among the number- 
left Species of Beings, vvhofe natural Lives are as fhort as this 
was fuppofed to be : fuch too are moft likely to be found 
amongft the very minute Kinds. For as thofe 'exceeding/mail 
Plants , invifible to the naked Eye, which compofe what we 
call Mouldinefs, fpring up, bear Fruit, and die in a few 
Hours ; we may reafonably fuppofe the Lives of fome ex¬ 
ceedingly fmall Animals to be of as fhort a Duration. 
