Concerning the venomous Urine of Toads, of the stone in the Toads head, and of the generation of Frogs, conceptions are entertained which require consideration. And first, that a Toad pisseth, and this way diffuseth its venome, is generally received, not only with us, but also in other parts; for so hath _Scaliger_ observed in his Comment, _Aversum urinam reddere ob oculos persecutoris perniciosam ruricolis persuasum est_; and _Mathiolus_ hath also a passage, that a Toad communicates its venome, not only by Urine, but by the humidity and slaver of its mouth; which notwithstanding strictly understood, may admit of examination: for some doubt may be made whether a Toad properly pisseth, that is distinctly and separately voideth the serous excretion: for though not only birds, but oviparous quadrupeds and Serpents have kidneys and ureters, and some Fishes also bladders: yet for the moist and dry excretion they seem at last to have but one vent and common place of exclusion: and with the same propriety of language, we may ascribe that action unto Crows and Kites. And this not onely in Frogs and Toads, but may be enquired in Tortoyses: that is, whether that be strictly true, or to be taken for a distinct and separate miction, when _Aristotle_ affirmeth, that no oviparous animal, that is, which either spawneth or layeth Eggs, doth Urine except the Tortois. The ground or occasion of this expression might from hence arise, that Toads are sometimes observed to exclude or spit out a dark and liquid matter behind: which we have observed to be true, and a venomous condition there may be perhaps therein, but some doubt there may be, whether this is to be called their urine: not because it is emitted aversly or backward, by both sexes, but because it is confounded with the intestinal excretions and egestions of the belly: and this way is ordinarily observed, although possible it is that the liquid excretion may sometimes be excluded without the other. As for the stone commonly called a Toad-stone, which is presumed to be found in the head of that animal, we first conceive it not a thing impossible: nor is there any substantial reason why in a Toad there may not be found such hard and lapideous concretions. For the like we daily observe in the heads of Fishes, as Cods, Carps, and Pearches: the like also in Snails, a soft and exosseous animal, whereof in the naked and greater sort, as though she would requite the defect of a shell on their back, Nature near the head hath placed a flat white stone, or rather testaceous concretion. Which though _Aldrovandus_ affirms, that after dissection of many, he found but in some few: yet of the great gray Snails, I have not met with any that wanted it: and the same indeed so palpable, that without dissection it is discoverable by the hand.