To convert this hypothesis into a demonstration, Von Berlepsch invited to his apiary in succession the two great comparative anatomists Professors Leuckart and Von Siebold, and furnished each with a number of both drone and worker eggs for microscopic examination. Leuckart examined the surfaces of the eggs; Von Siebold, who followed him, tried the interiors, and the latter by this means was triumphantly successful, for, after the most careful preparation of his subjects, he detected in thirty out of forty worker eggs from one to four spermatozoa apiece, while in his twenty-four drone eggs he found not a single one. The exceptions were insufficient to invalidate the results, for the ten worker eggs in which no signs of impregnation were found were only the failures of observation to be naturally expected in so delicate a scrutiny. Thus the fact was established that eggs which produce male bees are descended from the female only--in other words, that _drones have no fathers!_ Most strikingly has this law been corroborated by a discovery which we owe to the introduction of the Italian bee--a discovery, too, which any bee-keeper can make for himself. If an Italian queen is crossed with an English drone, or _vice versa_, the _workers only_ of her progeny will be mongrels--the drones will invariably retain the pure blood of the queen, thus proving to demonstration that they owe their origin to her alone. Should a mongrel drone be then observed, it will be a sure sign that a fertile worker is in the hive: the queen will not be its mother. Dr. Dönhoff, we are told, confirmed the same law by a converse method, having in 1855 obtained a worker bee from a drone egg which he had artificially impregnated with the male fluid. The queen, as we have observed, is capable before fertilisation of becoming the mother of drones, but it is believed by some that if she has once commenced drone-laying it is impossible for her to become subsequently fertilised. Mr. Langstroth, however, mentions an instance to the contrary, where a queen of his, after persistently laying drone eggs for a week or two, became after that the happy mother of a thriving colony of workers. Von Berlepsch alludes to this case (with others like it), but is unconvinced, being suspicious that here again it was a fertile worker and not the queen who laid the drone eggs. But looking to the fact that many _permanently_ unfertile queens lay drone eggs, while others lay no eggs at all, does it not seem reasonable that a similar difference may subsist _previous_ to fecundation? Thus, while the Baron is on firm ground as to the general rule, we incline to a belief that as to the exception the American observer is quite correct.