& 
: 
—— 
— 
il , 
ty . See = 
et 
cl 3, 1923] 
NATURE 
287 

- there seems very little room or need for subsidiary 
mechanisms of heredity. The cytoplasm presumably 
has its functions in this regard ; but the absence of 
accuracy in cytoplasmic division, together with the 
presence of this large battery of genes in the accur- 
ately divided chromosomes, make us sceptical as to its 
Se many *‘ heredity-determining "’ substances. 
inally, there is no reason to doubt and a good 
deal of reason to believe that all higher animals and 
lants possess chromosomal gene-complexes similar 
in essentials of structure and working to that so 
thoroughly analysed in Drosophila. 
Juitan S. Huxvey. 
New College, Oxford, 
February 4. 

Age and Area and Natural Selection. 
I am not especially eager to defend Dr. Willis’s 
theory of ‘‘ Age and Area.’’ My chief interest in 
. Dr. Willis’s views is that they agree with those of 
Dr. W. Bateson and myself in accepting and confirm- 
ing the conclusion that the distinctions of species have 
as a rule nothing to do with adaptation, and therefore 
nothing to do with Natural Selection. 
Dr. Clark states (NATURE, February 3, p. 150) that 
every systematic zoologist whom he knows believes in 
Darwin’s theory. But I long ago became convinced 
that the knowledge of systematic zoology, however 
profound and however accurate, confers no right to, 
and affords no justification for, the expression of 
opinions on questions of evolution, or at least on the 
causes and processes of evolution. To form a 
judgment on such questions requires certainly know- 
ledge and experience of systematic zoology, especially 
of its principles and of the species in some particular 
group or groups of animals, but it also requires a 
practical knowledge of modern researches in genetics, 
of cytology, of certain branches of physiology, and 
of the life and habits of some group or groups of 
animals. 
At the present time zoologists are usually specialists, 
and each specialist gives forth conclusions about 
problems of evolution based almost exclusively on 
the phenomena of his own special study. Dr. 
Bateson believes that no facts are of any great 
importance except those of genetics, that is to say, of 
the behaviour of characters in experimental breeding, 
and pays little or no attention to the question of 
adaptation. Prof. MacBride, on the other hand, a 
specialist in embryology, asserts that the characters 
and mutations studied by geneticists are merely 
pathological, and that all natural varieties are dis- 
tinguished by differences of adaptation, due presum- 
ably to the action of external conditions. Dr. Clark 
apparently believes that diagnostic characters are all 
adaptive and to be explained by Natural Selection. 
Dr. Clark states that his own special group is that 
of echinoderms. I wonder whether he has studied 
the mode of life of the species and varieties of echino- 
derms in Nature, and if he could bring forward any 
evidence to show a correlation between specific 
differences and differences of habit and mode of life. 
Many of the older systematists, holding no brief for 
any theory, recognised (and I think correctly) that 
there is a general distinction between characters which 
show natural affinities and are therefore most im- 
“portant in classification, and adaptive characters 
which are related to habits and conditions. Natural 
Selection is a theory of the origin of adaptations, and 
in my judgment there is ample evidence that specific 
differences are not as a rule differences of adaptation. - 
Therefore Natural Selection does not explain specific 
differences. 
NO. 2783, VOL. T11] 
It is recognised now that in the cultiva- 
tion of animals and plants the marked and constant 
characters which distinguish races are not, as Darwin 
believed, the gradual result of continued selection, 
but are mutations which have arisen spontaneously 
in definite form, not by successive stages. Does any 
one believe now that the rose comb in fowls is the 
result of a series of stages due to artificial selection ? 
If Dr. Clark would do me the honour of reading my 
book ‘‘ Hormones and Heredity,’’ he would find these 
matters more fully discussed, and would perhaps 
understand better why I consider the theory of 
Natural Selection to be obsolete. That conclusion, 
of course, is not disproved by the fact that many 
naturalists still believe in the theory, in America and 
elsewhere. But there are specialists in evolution as 
well as in systematic zoology and in other branches, 
and I venture to say that few who have made a special 
and practical study of evolution and are well acquainted 
with recent progress in that study, have much faith 
in Natural Selection. 
It is evidence which is important rather than 
opinions, and I would ask what evidence Dr. Clark 
can bring forward to prove the adaptive value of 
specific and other diagnostic characters in echino- 
derms. Personally I am not interested in the 
explanation of the origin of species, but in the origin 
of the particular characters which distinguish one 
species from another. J. T. CUNNINGHAM. 
University of London Club, 
21 Gower Street, W.C., 
February 5. 

The Value of e/m. 
Ir is quite customary, at the present time, to use as 
the most probable value of e/m that derived by Paschen 
from spectroscopic data, as given by equations (12) and 
(13), page 272, and (15) and (16), page 275, of Sommer- 
feld’s ‘‘ Atombau,”’ third edition. Taking Paschen’s 
own estimate of the error in Ry. and Ry, we have a 
probable error in e/m of about 0-2 per cent. But I 
have shown by a more detailed consideration of all 
available data (Physical Review, 17, 589, 1921) that 
Paschen's estimate of error for Ry (+0-06) is certainly 
too small, and that the true probable error is nearer 
+o-2. The latter figure leads to an error of 0-5 per 
cent in e/m, and the Paschen data, combined with the 
best data on atomic weights (4-002 and 1-0077 for 
He and H) result in e/m=1-768+0-009, where the 
error in Ry has alone been considered. 
Paschen used older and less accurate values for 
the index of refraction of air, in his reduction to 
vacuum. With the new values Bell (Philosophical 
Magazine, 40, 489, 1920) has shown that the value of 
Rue is raised 0-17 to 109,722-31. Since the calculation 
of this constant is independent of any particular 
assumptions as to the relative intensity of fine 
structure components, it is probable that this revised 
value is quite trustworthy, and I shall assume Paschen’s 
own estimate of error, 40-04. The calculation of 
Ry is much more uncertain. Using the original 
Sommerfeld theory, as Paschen did, but all available 
data and the newer values for the reduction to 
vacuum, I have shown (loc. cit.) that Paschen’s value 
of Ry is raised 0-14, to 109,677°826. But experimental 
results agree more closely with the more rational 
Bohr theory as to the intensity relations, and this 
theory yields a value of Ry lower by o-21. Any 
lowering of the 2 to 1 intensity ratio of the Balmer 
series components leads to a lower value of Ry. I 
have suggested 109,677-7 as the most probable value 
of Ry, this being the mean value yielded by various 
theories. This value, combined with Bell’s revised 
value of Rue gives 1-762 for e/m. 
