Breeding in-and-in has some advantages and many advocates. It is a knotty point to touch upon. At the commencement I stated that my own experience led me to adopt a middle course; that experience has not been in favour of the system. By adhering to it I found that quality was maintained, and even improved; but size was reduced, and symptoms of delicacy of constitution were manifested. It may be pursued for a time, until the type is developed, but to continue for any length of time to breed _in_ and in, is not only against my experience, but, I believe, against nature. In looking over a herd of breeding cattle, I have often seen the owner or the cattle-keeper pointing out a cow that throws a good calf, and never threw a bad one, and at the same time telling you how great a milker she is. It would be difficult to buy such a cow too dear. Most of the above remarks may apply alike to the home farm of the proprietor, to the large and small farmer, and to the crofter with one cow. It is well known to breeders of cattle, and I believe of sheep, that there are particular races that are celebrated, and upon which you can calculate that they will never propagate an inferior animal. Specimens not so desirable will now and again appear, but the blood is there, and the divergence will not be great from the desired type. Again, there will be one race noted for producing celebrated males, and another for producing celebrated females. A bull may be introduced that is a great getter of bull calves, yet the change may not be to the advantage of the owner, as the female calves will not be bred of so high an order. Professor Thury, of Geneva, has written a very interesting paper on the law of the production of sexes. In a letter to me, dated 14th February 1864, he says: "There are, if the owner pleases, two periods of heating: the one the general period, which shows itself in the course of the year, following the seasons; the other, a particular period, which lasts in cows from twenty-four to forty-eight hours, and which reveals itself a certain number of times. It is this particular period, lasting from twenty-four to forty-eight hours, the commencement of which gives females, while its termination gives males. In order that we may obtain a certain result, we must not cause the same cow to be covered twice in succession at an interval too short, for the (generative) substance of the bull preserves itself for a time sufficiently long in the organs of the cow. In the experiments made in Switzerland we have taken the cow at the first certain signs of heating, for the purpose of obtaining heifers, and at the termination of the heating for the purpose of obtaining males. The result of these experiments is, that we do not yet know what is the relative length of time which gives females, and the time which gives males; this would form an interesting subject of examination. I am of opinion that various circumstances must be regarded as influencing the relative