Among the "faint rays" alluded to by Mr. Darwin as throwing light upon the changes dependent on the laws of reproduction, there is one, perhaps the brightest yet seen, which deserves our notice. It is the apparent influence of the male first having fruitful intercourse with a female upon her subsequent offspring by other males. Attention was first directed to this by the following circumstance, related by Sir Everard Home: A young chestnut mare, seven-eighths Arabian, belonging to the Earl of Morton, was covered in 1815 by a Quagga, which is a species of wild ass from Africa, and marked somewhat in the style of a Zebra. The mare was covered but once by the Quagga, and after a pregnancy of eleven months and four days gave birth to a hybrid, which had, as was expected, distinct marks of the Quagga, in the shape of its head, black bars on the legs and shoulders, &c. In 1817, 1818 and 1821, the same mare was covered by a very fine black Arabian horse, and produced successively three foals, and although she had not seen the Quagga since 1816, they all bore his curious and unequivocal markings. Since the occurrence of this case numerous others of a similar character have been observed, a few of which may be mentioned. Mr. McGillivray says, that in several foals in the royal stud at Hampton Court, got by the horse "Actaeon," there were unmistakable marks of the horse "Colonel." The dams of these foals were bred from by Colonel the previous year. A colt, the property of the Earl of Suffield, got by "Laurel," so resembled another horse, "Camel," that it was whispered and even asserted at Newmarket that he must have been got by "Camel." It was ascertained, however, that the mother of the colt bore a foal the previous year by "Camel." Alex. Morrison, Esq., of Bognie, had a fine Clydesdale mare which in 1843 was served by a Spanish ass and produced a mule. She afterwards had a colt by a horse, which bore a very marked likeness to a mule--seen at a distance, every one sets it down at once as a mule. The ears are nine and one-half inches long,--the girth not quite six feet, stands above sixteen hands high. The hoofs are so long and narrow that there is a difficulty in shoeing them, and the tail is thin and scanty. He is a beast of indomitable energy and durability, and highly prized by his owner. Numerous similar cases are on record,[6] and it appears to have been known among the Arabs for centuries, that a mare which has first borne a mule, is ever after unfit to breed pure horses;[7] and the fact seems now to be perfectly well understood in all the mule-breeding States of the Union. A pure Aberdeenshire heifer, the property of a farmer in Forgue, was served with a pure Teeswater bull to which she had a first cross calf. The following season the same cow was served with a pure Aberdeenshire bull, the produce was in appearance a cross-bred calf, which at two years old had long horns; the parents were both hornless.