Experiments on mice also showed that the cutting off of the tail, even when performed on both parents, does not bring about the slightest diminution in the length of tail in the descendants. I have myself instituted experiments of this kind, and carried them out through twenty-two successive generations, without any positive result. Corroborative results of these experiments on mice have been communicated by Ritzema Bos and, independently, by Rosenthal, and a corresponding series of experiments on rats, which these two investigators carried out, yielded the same negative results.
When we remember that all the cases which have been brought forward in support of an inheritance of mutilations refer to a _single_ injury to one parent, while, in the experiments, the same mutilation was inflicted on both parents through numerous generations, we must regard these experiments as a proof that all earlier statements were based either on a fallacy or on fortuitous coincidence. This conclusion is confirmed by all that we know otherwise of the effects of oft-repeated mutilations, as for instance the well-known mutilations and distortions which many peoples have practised for long, sometimes inconceivably long, ages on their children, especially circumcision, the breaking of the incisors, the boring of holes in lip, ear, or nose, and so forth. No child of any of these races has ever been brought into the world with one of these marks: they have to be re-impressed on every generation.
The experience of breeders agrees with this, and they therefore, as Wilckens remarks, have long regarded the non-inheritance of mutilations as an established fact. Thus there are breeds of sheep in which, for purely practical reasons, the tails have been curtailed quite regularly for about a century (Kühn); but no sheep with a stump-tail has ever been born in this breed. This is all the more important because there are other breeds of sheep (fat-rumped sheep) in which the lack of the tail is a breed character; it is thus not the case that there is anything in the intrinsic nature of the tail of the sheep to prevent it becoming rudimentary. The artificially rounded ear of fox-terriers, too, though cut for generations, never occurs hereditarily. Mr. Postans of Eastbourne informs me that the cocks which are to be used for cock-fighting are docked of their combs and wattles beforehand, and that this had been done for at least a century, but that no fighting cock without comb and wattles has been reared. In the same way various breeds of dog, such as the spaniels, have had their tails cut to half their length regularly and in both sexes for more than a century, yet in this case there is no hereditary diminution of the length of tail. Deformed stump-tails do indeed occur in most breeds of dog, but, as I said before, their anatomical character is quite different from that of artificially shortened tails, moreover they may occur in breeds whose tails have not suffered from the fashion of docking, as, for instance, in the Dachshund.