There are cows with very small mirrors, which are, nevertheless, very fair in the yield of milk; and among these with middling quality of mirrors instances of rather more than ordinary milkers often occur, while at the same time it is true that now and then cases occur where the very best marked and developed mirrors are found on very poor milkers. I once owned a cow of most extraordinary marks, the milk-mirror extending out broadly upon the thighs, and rising broad and very distinctly marked to the buttocks, giving every indication, to good judges, of being as great a milker as ever stood over a pail; and yet, when she calved, the calf was feeble and half nourished, and she actually gave too little to feed it. But I believe that this exception, and most others which appear to be direct contradictions, could be clearly explained by the fact, of which I was not aware at the time, that she had been largely over-fed before she came into my possession. I mention this case simply to show how impossible it is to estimate with mathematical accuracy either the quantity, the quality, or the duration of the milk, since it is affected by so many chance circumstances, which cannot always be known or estimated by even the most skilful judge; as the food, the treatment, the temperament, accidental diseases, inflammation of the udder, premature calving, the climate and season, the manner in which she has been milked, and a thousand other things which interrupt or influence the flow of milk, without, materially changing the size or the shape of the milk-mirror. M. Magne, who appears to me to have simplified and explained the system of Guénon, and to have freed it from many of the useless details with which it is encumbered in the original work, while he has preserved all that is of practical value, very justly observes that we often see cows, equally well formed, with precisely the same milk-mirror, and kept in the same circumstances, yet giving neither equal quantities nor similar qualities of milk. Nor could it be otherwise; for, assuming a particular tuft on two cows to be of equal value at birth, it could not be the same in the course of years, since innumerable circumstances occur to change the activity of the milky glands without changing the form or size of the tuft; or, in other words, the action of the organs depends not merely on their size and form, but, to a great extent, on the general condition of each individual. Te give a more distinct idea of the milk-mirror, it will be necessary to refer to the figures, and the explanations of these I translate literally from the little work already referred to, the _Choix des Vaches Latières_, or, the Choice of Milch Cows.