September 29, 1904] 



NA TURE 



539 



rcL-iprocally with an inbred pair of Belgian hares (F,), and 

 the hybrid progeny were bred with one another for two 

 generations (K. and !• ,). In K, the Angora coat was always 

 recessive to the normal coat, and the albino character re- 

 cessive to the normal character, while in K, and F, both 

 these features followed the ordinary Mendelian rules. As 

 to coat colour, in F, the first cross of brown and albino 

 gave offspring all of which had wild grey coats. In F, the 

 hybrid greys bred together gave a ratio of 9 grey : 3 black : 

 4 albino, which, when worked out in detail, is in accordance 

 with the Mendelian expectation. Experiments on Fj proved 

 that the black factor was not introduced by the original 

 brown parent, but by the albino, which, though gametically 

 pure as regards simple albinism, was at the same time 

 carrying the distinct factor for black coat colour. 



Prof. Weldon, in opening the discussion, referred to one 

 of -Mendel's experiments in which he took a pea of a race 

 producing only seeds with green cotyledons and crossed it 

 with one of another race producing only seeds with yellow 

 cotyledons. The resulting seeds produced plants a quarter 

 of which bore green seeds only, a quarter yellow seeds only, 

 and each of these sets was said to breed true. The remain- 

 ing half produced seeds with the hybrid properties of their 

 immediate cross-bred parents. Considering how reversion 

 has been found by Mr. Galton in other cases, we might re- 

 gard the hybrids which made up half the segregation gener- 

 ation as reverting directly to their parents, and the remain- 

 ing half as reverting to the various green-seeded or yellow- 

 seeded ancestors in various proportions, so that every gener- 

 ation of ancestry was represented to a greater or less extent, 

 the nearer ancestors more frequently, the remoter more 

 rarely. In Mr. Bateson's translation Mendel says that the 

 yellow-seeded individuals reproduce the character of the 

 yellow-seeded " parent form," but we do not know whether 

 -Mendel meant the race or one individual of the race. Mr. 

 Bateson and others have adopted the view that, so far as 

 colour is concerned, the green-seeded and the apparently 

 true-breeding yellow-seeded forms were not merely like, but 

 identical with the pure individuals of the green- or yellow- 

 seeded races used in making the original cross. The view 

 attributed to Mendel paid attention to the last two only of 

 the pure-bred ancestors, while that of Galton and others 

 considered that all the ancestors contributed in various pro- 

 portions to the characters of the subsequent generations. 

 The description of the seed colours is not accurate enough 

 to enable one to decide between these two hypotheses. 

 Because each human being, his parents and grandparents, 

 have seven cervical vertebr;e, we have no right to say that 

 we are exactly like our fathers, and that our grandfathers 

 have no share in determining our characters. Again, each 

 of the species included as Lychnis dioica has a hairy and 

 glabrous form, the plants resulting from a cross of which 

 are hairy, and the offspring of such hybrids are hairy or 

 glabrous in Mendelian proportions. But we are not told 

 how hairy either plant- is. Prof. Weldon counted the hairs 

 on pure-bred hairy plants, and found them to vary from 

 about a dozen to 1300 per sq. cm. of leaf surface. Now if 

 one with 1300 hairs per sq. cm. were crossed with a glabrous 

 plant, and if the offspring had on an average 500 hairs per 

 sq. cm., were they " hairy " like their hairy parent or com- 

 pletely intermediate between the two parents? Questions 

 of this kind required finer methods of observation and de- 

 scription. .Again, the frequent existence of reversions to 

 the characters of fairly reinote ancestors was inconsistent 

 with the idea that the characters of hybrids might be re- 

 garded as due to the combination of " pure " determinants 

 derived from their immediate parents. It had been said 

 that the numerical conclusions drawn from the Mendelian 

 hypothesis agreed so closely with the observed distribution 

 of the descendants of hybrid individuals that these alone 

 justified the conception of gametic purity. It was easy 

 with a small series of results to devise several hypotheses 

 which would fit the results. For example, crossing albino 

 and yellow mice of known ancestry, Cu(5not obtained 81 

 albino, 34 yellow, 20 black, and 16 grey mice, and the 

 remarkable modification of -Mendel's theory which he had 

 put forward to describe this result led him to predict the 

 numbers 76, 38, iq, and iq. This was not so good as Prof. 

 Pearson's prediction — 82-5, 31, 20.5, 17. In conclusion, he 

 argued that until further experiments and more careful de- 

 scriptions of results were available, it was better to use the 



NO. 1822, VOL. 70] 



purely descriptive statements of Galton and Pearson than 

 to invoke the cumbrous and undemonstrable gametic 

 mechanism on which Mendel's hypothesis rested. 



In the afternoon of -August 19 Mr. Punnett, on behalf of 

 Mr. Bateson, described the effects of crossing in fowls, and 

 Prof. Minot added some observations on his experiments 

 upon guinea-pigs. 



Mr. Bateson then replied in some detail to Prof. Weldon's 

 criticisms, and maintained that by the Mendelian hypo- 

 thesis alone was it possible to draw together the vast number 

 of observed facts which had seemed utterly incoherent. The 

 -Ancestrians, however, asserted that the laws based on 

 ancestry could cope with the same facts. Prof. Weldon had 

 passed very lightly over the critical fact which finally settled 

 the question — the purity of the characters of the segregated 

 types. None of the various schemes of the -Ancestrians had 

 contemplated such purity, and all were totally unable to 

 deal with it. The last attempt to explain away the fact of 

 purity of type was that enunciated to-day by Prof. Weldon, 

 who regarded it as " reversion." But if the " reversion " 

 were so complete as to include even the purity of the parental 

 type, such reversion was Mendelian segregation by another 

 name. The second fact with which the -Ancestrians could 

 not deal was the condition of those hybrids or heterozygotes 

 which, though again and again crossed back with pure 

 types, had always the same gametic constitution undiluted. 

 He illustrated this from the work of Mr. R. H. Lock on 

 maize, in which it was shown that, using mongrel 

 materials, as regards yellow and white grains, the inherit- 

 ance was of a normal Mendelian order. Sweet peas pro- 

 vided further illustrations of the applicability of Mendelian 

 principles to complex cases. It was shown that, in one 

 example, at least eight kinds of purple individuals occur in 

 the second generation, each having distinct powers of trans- 

 mission, though outwardly indistinguishable. Only minute 

 experiment could distinguish. these fundamental differences, 

 which the biometrical system entirely disregarded. The 

 evidence also included one significant case in which sterility 

 of the anthers behaved as a Mendelian character, and made 

 it possible to discriminate two types of extracted whites 

 almost certainly dissimilar in their powers of transmitting 

 colour-factors. Prof. Weldon had asked whether the ex- 

 tracted types showed parental characters unchanged. 

 Frequently the extracted types were- identical with the pure, 

 but the question must be answered case by case, accord- 

 ing to the special sort of segregation which took place in 

 each case. . The Mendelian theory had begun to coordinate 

 the facts of heredity, until then utterly incoherent and con- 

 tradictory. The advance made in five years had been 

 enormous, and he had no doubt of the result. 



Prof. Karl Pearson said that the great revolution which 

 Mr. Francis Galton introduced into biological study was 

 purely a difference of method. ■ The introduction of methods 

 of precision had nothing to do with Mendelism or ancestral 

 law. He had seen the -Mendelians produce figures without 

 making any attempt to show that the figures were con- 

 sonant with the theory they were supposed to illustrate. 

 He believed he had elaborated the most complete Mendelian 

 system ever yet worked out, but this led to general principles 

 which were singularly like those proposed by Galton from 

 observation. He asked from the Mendelians some definite 

 theory which could be worked out, and for further work, for 

 the controversy could only be settled by investigation, not 

 by disputation. 



-After some remarks by Prof. Hubrecht and Rev. 

 T. R. R. Stebbing, who said that interest in this important 

 inquiry was greatly quickened by the controversy, and hoped 

 it would continue, as from it the world could only gain the 

 light. Prof. Hickson (from the chair) closed the discussion 

 by saying that the subject in dispute was of the greatest 

 importance, and the debate had been of much value to those 

 biologists who were still " sitting on the fence." 



In the zoological laboratory there were numerous exhibits 

 of the specimens used in these various experiments on 

 heredity. 



At the invitation of His Grace the Duke of Bedford, a 

 party of twenty-five zoologists visited Woburn -Abbey on 

 .Saturday morning, August 20. The party was met by two 

 representatives of the Duke of Bedford, and driven over the 

 estate to see the splendid collection of animals there main- 

 tained in such excellent condition. Numerous species of 



