AUTHOR’ PREFACE 
URIOUS reader, before I proceed to lay my obfervations before you, 
I muft moft humbly requeft, that you will not be difpleafed, if in all 
this work I have only made ufe of my own obfervations, as a folid and 
immoveable foundation to build upon, and that from them I have deduced 
certain conclufions, folid theorems, and claffes digefted in due order. For 
as long as neither nature herfelf exhibits any thing in oppofition to thefe 
theorems, nor other writers produce experiments to contradict thems we 
may reft affured of the truth of what I have delivered; but then we mutt 
- not wander beyond the limits of fuch obfervations, nor by ftraining them 
too much, make them extend to things not as yet fufficiently difcovered. 
Otherwife, as nature is utterly inexhauftible, we fhould be in danger of fall- 
ing into errors; and indeed it is generally our own fault that things of them= 
felves fufficiently clear and evident, become obfeure, and even impenetrable 
to us. Thus a perfon would be guilty of a great miftake; who, after 
running over all the animals he knew, never to be at once male and fe- 
male, fhould from thence conclude, that both fexes are never found in one 
and the fame fubject ; whereas the contrary appears in Snails; which are all 
capable of impregnating as males, and conceiving as females, but with this 
reftri@tion, that the fame Snail cannot act upon itfelf; fo that a mutual inter- 
courfe of two is requifite to carry on the bufinefs of propagation, as I many 
years ago demonftrated before a numerous company. As therefore all the 
experiments I have hitherto made, agree perfe@ly together, and mutually 
fupport each other, there is the lefs reafon, till fomething appears in the 
nature of things to break the thread of my fyftem, to be ftartled at the 
objections of others, who never made the fame obfervations, and are not 
perhaps properly qualified to make the fame experiments. But if hereafter 
any thing fhould occur, that I may have reafon to think deferves to be added 
to what I have already advanced, or exceeds the bounds to which I have 
confined myfelf, or appears repugnant to my former obfervations; I promife 
faithfully to publifh them, though they fhould abfolutely deftroy the prin- 
ciples I have laid down, provided that they ferve to confirm and illuftrate 
the truth. And I moreover earneftly requeft all thofe who love truth as I 
do, and are equally anxious to find it out, to affift me on this occafion with 
their favour and advice. | 
But as the moft eminent amongft the ancient writers on this branch of 
natural hiftory, have propofed two different manners in which infe&s un- 
dergo their mutations; one known by the name of Nymph, and the other 
by that of Chryfalis, calling Nymph that change’cf the Worm, under 
which it exhibits the form of the infeé that is to iffue from it; and Chry- 
falis, that other change which fhews no figns of the future infeét; I mutt 
; forewarn 
