Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/290

246 that have been so fully verified as to rank with exact science, there are no inductions so trustworthy as those which have undergone the mercantile test. When we have thousands of men whose profit or loss depends on the truth of the inferences they draw from simple and per petually repeated observations ; and when we find that the inferences arrived at and handed down from generation to generation of these deeply interested observers has become an unshakeable conviction, we may accept it without hesi tation. In breeders of animals we have such a class, led by such experiences and entertaining such a conviction the conviction that minor peculiarities are inherited as well as major peculiarities. Hence the immense prices paid for successful racers, bulls of superior form, sheep that have certain desired peculiarities.&quot; Not only are slight and gradual changes inherited, but in some cases sudden and well-marked variations are strongly transmitted. The case of the Niata cattle is now well known ; a similar case is recorded of a rabbit born with only one ear, from which a breed was formed which steadily produced one-eared rabbits. These remarkable cases of sudden and large varia tion being inherited are closely allied to the still more curious phenomenon of the inheritance of mutilations. The most striking cases on record are those of Brown-Se quard. In his experiments on the inheritance of artificially produced epilepsy he found that guinea pigs, after having undergone section of the sciatic nerve, often nibbled off portions of their hind legs in consequence of the anaesthesia of those parts. Now the offspring of these self-mutilated animals were in thirteen cases born without toes. To appreciate the true value of this case it must be noted that Dr Brown- Sdquard has for thirty years kept guinea pigs, and has had many thousands under observation, and not a single case of congenitally toeless animals has occurred excepting among the offspring of mutilated parents. In spite of the uni versal tendency towards the transmission of the form and qualities of the parents to the offspring, there occur capri cious and inexplicable lapses in inheritance. It is not possible logically to distinguish a want of inheritance from a case of variation ; but when the difference between the offspring and the parent consists merely in the absence in the former of a quality possessed by the parent, it may be more conveniently classed as a want of inheritance than as an instance of variation. Although a weeping or pen dulous habit in trees is in some cases strongly inherited, in other instances the want of inheritance is equally well marked. Mr Rivers sowed above 20,000 seeds of the weep ing ash, and not a single seedling was in the least degree pendulous. M. Borchmeycr has also observed the same fact in Germany. In all cases it must be remembered that the form and qualities which the offspring of an animal or plant will assume when fully developed are not solely dependent on the nature of the hereditary impetus with which it starts ; the initial tendency is as it were calculated so as to impart under certain conditions a certain form to the organism. If the conditions change, the initial ten dency will not lead to the proper result ; and it is to be noted that the apparent amount of alteration in the con ditions is no measure of the amount of effect produced on the organism. For instance, none of the English breeds of sheep can be kept pure in France, the lambs of even the first generation lose vigour as the heat of the summer comes on, and the breed becomes absolutely degenerate. It is extremely curious that the force of inheritance which seems all powerful in England should give way so utterly under such a slight change of circumstances. The method by which a breed was formed, combining the valuable qualities of the English sheep with a consti tution fitted for the French conditions of life, is most instructive, and is a triumph of thoughtful and scientific breeding. The successful attainment of this end is due to M. Malingie -Nouel. He found that the offspring of a cross between a pure English ram and a French ewe inherit the desirable form of the sire, but, unfortunately, also his undesirable constitution. He accordingly paired a ewe taken from a border district, and therefore intermediate between two breeds, with a similar intermediate ram. He thus produced a sheep &quot; combining the four races Berry, Sologne, Merino, and Touraine. . . without decided char acter, without fixity,. . . but possessing the merit of being used to our climate and management.&quot; It was now found that the lambs born of this mongrel ewe by purely-bred New Kent rams combined the English form with the French constitution, and transmitted this desirable com bination to their offspring, and in this way the &quot; Charmoise &quot; breed was produced. In this instance it seems as if the tendencies supplied by the ewe formed so discordant a combination that no strong tendency resulted for any of the French forms to appear, so that the form of the English ram was strongly impressed on the offspring. On the other hand, the constitutional tendencies coming from the mother s side were not dis cordant, but united in impressing the French constitution on the offspring. This case is instructive as establishing the possibility of an important kind of acclimatization, and as bearing on a somewhat exceptional phenomenon of heredity, namely, that when both parents exhibit a given character strongly, the offspring do not inherit it so surely as when one ; parent only is especially well characterized. Thus a successful breeder of laced Sebright bantams says, &quot; I am confident that those that arc best laced frequently produce offspring very far from perfect in their markings, whilst those exhibited by myself which have so often proved successful were bred from the union of heavily laced birds with those that were scarcely sufficiently laced.&quot; The class of cases just noticed is, moreover, of great interest as bearing on a form of inheritance which has been named &quot;prepotency of transmission.&quot; When the offspring, instead of being intermediate between the parents, strongly resemble one of them, the latter is said to be prepotent in transmitting its likeness. The famous bull Favourite is believed to have had a prepotent in fluence on the short-horn race. It has also been observed with English race horses that certain mares have generally transmitted their own character, while other mares of equally pure blood have allowed the character of the sire to prevail. In other cases a remarkable weakness of transmission of character is found to exist. A striking instance is given by Mr Brent. It must be premised that the breed of pigeons known as &quot;trumpeters&quot; is characterized ~by a tuft of feathers over the beak, by a crest on the head, and by a most peculiar coo. Mr Brent crossed a trumpeter with another breed, and then recrossed the mongrels with trumpeters. But it was only at the fourth generation, when the birds had ^ trumpeter blood in their veins, that the characteristic tuft appeared, and even then the peculiar trumpeting coo was absent. It is frequently asserted that the male is prepotent over the female in transmitting certain characters. It has been shown, however, that such rules do not hold good except 