But what more strongly proves the truth of our explanation, is the resemblance of children to their parents. A son, in general, more resembles his father than his mother, and the daughter more her mother than her father; because a man has a greater resemblance to a man than to a woman, and a woman resembles more a woman than a man, in respect to the whole habitude of the body; but for the features and particular habits, children sometimes resemble the father, sometimes the mother, and sometimes both. They will have, for example, the father's eyes, and the mouth of the mother, or the complexion of the latter, and the size of the former; which is impossible to be conceived, unless it is admitted that both parents have contributed to the formation of the child, and that consequently there was a mixture of the two seminal fluids. I acknowledge that resemblances raised many difficulties in my own mind; before I had maturely examined the question of generation, I was prepossessed with ideas of a mixed system, by which it appeared that I could explain in a probable manner every phenomena, excepting resemblances, and these I thought I had found very specious reasons to doubt, and which deceived me a long time, until having minutely observed, with all the exactness I was capable of, a great number of families, and especially the most numerous, I have not been able to resist the multiplicity of proofs; it is only after being fully convinced in this respect, that I have began to think differently, and to credit what I now believe to be the fact. Besides, although I had found the mode to avoid those arguments that would be made on the subject of mulattos, mongrels, and mules, I could not be prevented from observing that every explanation, where a reason could be given for the phenomena, cannot be satisfactory; and I am now perfectly convinced that the objections which might be used with respect to them, as well as particular parental resemblances, instead of opposing would confirm my explanation. I now proceed to draw some consequences. In youth the seminal fluid is less abundant, although more stimulating; its quantity encreases to a certain age, because in proportion as we approach that age, the parts of the body become more solid, admit less nutriment, send back a greater quantity to the common reservoirs, and consequently produce a greater abundance of seminal fluid. When the external organs have not been used, persons of a middling age, and even old men, more easily engender than young ones. This is evident in the vegetable system, the older a tree is, the more fruit or seed it produces.