There are therefore animals, distinguished by sexes, which have proper parts for copulation, and some which are deficient in them; others, as snails, have both, and the two sexes in the same individual; others, as vine-fretters, have no sex, and engender in themselves separately; although they couple together when they please, we cannot determine whether that is a conjunction of sexes; if it is so, we must suppose that Nature has included in this small individual more faculties for generation than in any other kind of animal, and that it not only has the power of reproducing distinctly, but also the means of multiplying by the communication of another individual. But whatever difference takes place in generation, Nature, by a new production, prepares the body for it, and which, whether manifested outwardly, or concealed internally, always precedes generation. The ovaries of oviparous animals, and the testicles of female viviparous animals, before the season of impregnation, experience a considerable change. Oviparous animals produce eggs, which at first are attached to the ovaries, by degrees they increase in size, until they fall into the canal of the matrix, where they acquire their white membranes, and shell. This production has marks of the fecundity of the female, and without which generation cannot be performed: so in viviparous females there are always one or more glandular bodies on the testicles, which by degrees grow under the membrane that surrounds them; these glandular bodies enlarge and pierce, or rather impel and lift up the membrane of the testicle; when their maturity is complete, a small slit or several small holes appear at their extremities, by which the seminal liquor escapes, and falls into the matrix: these glandular bodies are new productions that precede generation, and without which there would not be any. In males there is also a similar change which always precedes their capacity for generating. In oviparous animals a great quantity of liquor fills a considerable reservoir, and which reservoir itself is sometimes formed every year; as in the calmar and some other fish. The testicles of birds swell surprisingly just preceding their amorous season. In viviparous males the testicles also swell considerably in those who have seasons, and in general there is a swelling and an extension of the genital members in all species, which, although it be external, must be regarded as a new production necessarily preceding generation.