In this case it very likely happened--as in such experiments it very easily may happen--that, in consequence of insufficient practical knowledge on the part of the experimenter, the actual commencement of the rutting time was overlooked. In addition, it is well known that animals, in consequence even of an amount of exercise not very exhausting, and in many other ways, as well as in consequence of the food they have taken, may exhibit variations in the activity of their rutting. It is not, therefore, surprising if the results of experiments show much that was unexpected. I here pass over a great number of proofs which Thury gives in his essay. Funcke (1866) made in his ‘Physiology’ the following remarks on Thury’s theory:--“Although the origin and determination of sex is not indisputably proved to depend upon the degree of ripeness of the ovum, it appears to me that we have not reached the right time for determining the factor upon which it does depend. These experiments have been made to repose upon a fact, which fact certainly proves, beyond the possibility of dispute, a relation between the fertilization of the ovum and the subsequent sex. This fact is that, in the case of certain creatures capable of parthenogenesis (unisexual procreation), we find that, from unfertilized ova one sex always results, and from fertilized ova the other. But any closer interpretation of this function of the semen is rendered nugatory in advance by this, that it is in some cases the male and in others the female that results from the unfertilized ova.” * * * * * Thury’s theory can be very suitably brought into agreement with the theory of cross-heredity of sex, and explained by the assistance of that view. The cow, at the beginning of her rutting, is not in a condition of great sexual vigor. If the ovum be effectually fertilized, it may be supposed that the bull, in procreative activity the superior consort, will be fitted not to reproduce his own sex, but that of the weaker cow. At the end of the rutting period the cow, which is brought to the bull, has her ovum ripened to the highest possible degree, and in consequence, when compared, from a sexual point of view, with the bull, is distinctly the stronger and superior, and a male calf is in this case the result of conception. According to the theory of cross-heredity of sex, female creatures should in the former instance be produced, and in the latter males, which same result is reached in accordance with the theory of Thury.