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 HEREDITY

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HEREDITY

Scientia Sinensis latine exposita studio et opera Pros- peri Intorcetta, Christiani Herdtrich, Francisci Rouge- mont, Philippi Couplet, PP. Soc. Jesu" (Paris, 177S). This earliest translation and elucidation gave Euro- pean scholars their first insight into the teachings of the Chinese sage. Herdtrich was also the author of a large Chinese- Latin dictionary (Wentse-Ko), proba- bly one of the first of its kind. The last nine years of his life were spent as superior of the mission of Kiang- tcheon, province of Shan-si. Emperor Kang-hi him- self composed his epitaph (cf . " Welt^Bott ", Augsburg, 1726, Nos. 16, 49).

HuoNDER, Deutsche Jesuitenmismontire (Freiburg im Br., 1899), ISS; Dahlmann, Die Sprachenkunde und die Missionen (Freiburg im Br., 1891), 32-37; Hazaut-Sontermans, Kir- chenaesch., I (\'ienna and Munich, 1707), 706 sqq. Letters oi Herdtrich may be found in; Intorcett.\, Compendiosa Narra- tione della Missione Cinense (Rome. 1672), 115-126; Greslon, Histoire de la Chine sous la domination des Tartares (Paris, 1670), 56; Katlml. Missionen (Freiburg im Br.) for 1901-02, pp. 25 sqq.; 1904-05, pp. 4 sqq.

A. HuONDER.

Heredity. — The offspring tends to resemble, some- times with extraordinary closeness, the parents; this is heredity. This definition omits the cases of (1) alternation of generations, where the offspring re- sembles a more remote ancestor in the direct line, the alternation being in regular or irregular rhythm; (2) the production of neuters, like their equally neuter uncles and aunts but unHke their (fertile) parents. On the other hand there is almost always, amongst higher forms at any rate, a certain unlike- ness as well as a likeness; this is variation. In these two sentences is summed up most of what is absolutely certain respecting these two subjects in spite of the enormous amount of attention which has been devoted to them and the voluminous literature consecrated to them. Some have conceived these two processes as at variance with one another, but this conception is false or at least wholly inadequate. Two methods are employed in studying the processes of heredity, the biometrical method, which seeks to work out the problem by mathematical means, and the method which follows the lines laid down by Abbot Mendel of Brunn (q. v.), whose long-forgotten obser- vations have led to many very profitable results and give greater hope of a real solution of the difficult questions involved in the subject of heredity than any others which have so far been made public. Particu- larly do they seem to throw light upon the much-dis- cussed but most imperfectly explained matter known as reversion. Where a unicellular organism divides into two cells it is hard to say which is mother and which is daughter, but there is no difficulty in under- standing why both of them closely resemble the cell from which both of them have been derived since lioth of them are that cell or part of it. This is heredity in its simplest terms. The matter becomes more com- plicated when the descendant is the offspring of a multicellular organism, even asexually, and infinitely more complicated when ordinary sexual reproduction comes into question. In the asexual case, however, if it could be shown that in the first division of an ovum a certain portion of the substance was set aside for future reproductive purposes, and that this was always the case, the condition would approximate to that of the unicellular organism above mentioned and the heredity would be explained by the fact that the off- spring was actually a portion of the original ancestor. Similarly in sexual reproduction, though the mat- ter is more complex, still the offspring would be the result of two ancestors whose reproductive sub- stance had been handed down in the manner indi- cated above.

This is practically Weismann's "germ-plasm the- ory". He supposes that each individual con.sists of two portions, somato-plasm, making up the main portion of the body, and germ-plasm stored away in

the sex-gland. This last he believes arises always from germ-plasm, that substance being set aside at the earliest stages of development and finally deposited in the sex-gland, when that organ becomes developed. It is obvious that this theory of a potentially immortal germ-plasrn entails great difficulties when the ques- tion of variation and especially variation induced by environment, comes into consideration. Moreover, there is no available evidence in higher forms that there is any such setting aside of germinal substance at early stages of development, and all the facts o{ regeneration are against the theory, as has been pointed out by Hertwig, Weismann's great opponent. If it be true, as it undoubtedly is, that a hydra, cut into several pieces can produce as many new individuals, and a begonia, by cuttings, propagate any number of new plants, it is difficult to see how it can be argued that all the reproductive sub- stance is .stored up in one only portion of the ani- mal or plant. Weismann's views, which have un- doubtedly exerted great influence on biologists and at one time met with a very large amount of accep- tance, have, it must be admitted, failed to meet a great deal of the criticism which has been directed against them, and do not at all hold the position which they occupied some years ago in scientific favour.

Another method of explaining heredity is that which presupposes that fragments from the different portions of the body become aggregated in the sex- cells and thus become the progenitors of the different portions of the offspring. Darwin's theory of "pan- genesis" and other similar explanations are of this character, and of them it may be said that they not only rest upon no demonstrable evidence but require so complicated a machinery as to become practically inconceivable. There remains the remarkable theory of "unconscious memory" put forward by Hering, and more recently by Semon and Francis Darwin, and developed in the writings of Samuel Butler. P.sy- chological explanation seems destined to receive more attention in the future than it has in the piist. Much doubt remains as to what portion of the cell is the bearer of the hereditary characteristics. Some years ago it was firmly held that these were borne by the nucleus, and further, by the chromosomes of the nucleus alone. Recent experiments have tended to make this theory, if not untenable, at least most doubtful, and it now seems that it may be the nucleiis, the protoplasm, orthecentrosome.or a combination of any or all of these, which may be held to occupy this position, if indeed it must be held that some definite part of the cell has to be indicated. The inheritance of acquired conditions is a point around which con- troversy rages and has raged for some time. It may at least be said that Weismann has proved, as far as such a matter can be proved, that mutilations are not inheritalile and this may be said in spite of the still doubtful explanation of Brown-S(^'quard's experi- ments in connexion with the production of epilep.^y in guinea-pigs. Weismann denies the possibility of the inheritance of acquired characters and has invented a cumbrous and, many would say, fanciful explanation to account for variation otherwise. Haeckel, on the contrary, would rather, as he says, believe in the Mosaic theory of creation than doubt the inheritance of acquired conditions.

This matter has often been complicated by the question of inherited disease, which is a wholly differ- ent question and of which all that can here be said is that, where it is not a case of bacterial or toxic infec- tion of the germ, it is not the di.sease which is inherited, but a certain character, or organ, or structure which renders its owner predisposed to the attacks of that disease, should he come in its way. As to the true inheritance of acquired conditions, however, there is, as above indicated, great difference of opinion, the