fince the production of the former, which 'devoured and 
lived upon the larger worm. 
In the middle of July Mr. Leeuwenhoek cropt feveral 
willow-leaves, in which were fuch like knobs p , and 
difcovered feveral worms nearly arrived to their full 
growth: after thefe knobs had been in the glafs tubes 
about eight days, upon opening one of them he found, 
that the worm was turned into a tonnekin or aurelia, and 
In fome others thirteen or fourteen more of the fame. In 
fome of the knobs he found the fmall devouring worms 
above-mentioned, being fo far advanced in growth that 
they were ready to be changed into flying infers 5 he put 
thefe alfo in glafs tubes. After fome weeks certain black 
flies proceeded from thofe tonnekins, their hinder parts of 
an oblong figure, and falhioned like a hook. He alfo 
faw two of thefe fmall worms (which devoured the large 
ones) endeavouring to enclofe themfelves in a web ; but 
by reafon of the large fpace in which they lay, could not 
bring it quite round them, having made it only on one 
fide, and their change happened in fo fhort a time that 
be could hot make his remarks thereon. 
Fig. 97. reprefents the aforefaid fly as it appears to the 
naked eye. A B {hews the long, flender, and hooked 
part; on examining this little inftrument in the microf- 
cope, it appeared to be hollow, and was covered with a 
great number of'fine hairs, as in fig. 98. and on en¬ 
deavouring to fplit it, the dart, fig. 99. appeared, whofe 
point is only jagged with faw-like teeth, which being 
alfo fplit, ■ two other diftindf hooks s were taken out of 
it both of the fame fhape, a fmall part of one of them is 
reprefented by fig; 100. each of them being fortified with 
faw-like teeth, and the dart fig; ror, was found to be 
only a fecond cafe or {heath for the two hooks, wherein 
* the 
* Phil, Tranf, No, 260. ^ Arc, Nat, Epift. 136. 
/ 1 
