









Medical Education. 
I REGRET that I have not the time to do justice to 
Sir Archdall Reid's last letter, which is supposed to 
deal with the above subject (NATURE, January 13, 
'p. 50). Itis, as I expected, really an attempt to open 
p another discussion on evolution. Now since Sir 
Archdall confesses to having already spent eighteen 
ths vainly trying to find out what biologists mean, 
it seems inadvisable to begin again; for his letter 
indicates a very imperfect acquaintance with biolo- 
gists and their work. 
To my mind it is an amazing suggestion that 
zoologists and botanists are incapable of teaching 
evolution, and it is illuminating indeed to find that 
men are to come after them ‘‘ who have observed, with 
a minuteness and accuracy “page to workers 
among plants and animals.” I shall be glad to meet 
! when they arrive. Meanwhile, until 
enappear, it is highly desirable that first- 
yea icals, raw youths from school, should make 
their first acquaintance with the animal world through 
less expensive material than human bodies, and should 
pproach a great profession with, what practice and 
theory have shown to be, the best introduction. 
- W. J. Dakin. 
Department of Zoology, University, 
Liverpool, January 17. 

















































_An Overlooked Feature in Four-legged Tadpoles 
of Rana temporaria. 
_ Att accounts of the metamorphosis of the common 
frog leave it to be tacitly inferred that when the 
mt legs make their way through the operculum 
anchial respiration ceases, and that thenceforth 
eathing is effected by the lungs, skin, and mucous 
embrane of the mouth. It appears to have been 
ely overlooked that from the time of the acquisi- 
free front legs until the tail is completely 
= absorbed, and the little anurous frog 
leaves the water, branchial respira- 
tion continues, water being drawn 
through the nostrils into the mouth, 
and discharged from the opercular 
chamber through a pair of crescentic 
apertures, one on each side immedi- 
rae anterior to the base of the front 
eg. 
In July 1922 I was watching some 
tadpoles that had just acquired their 
front legs, and was keeping them in 
a shallow dish of pond water in which 
was a certain amount of suspended, 
finely divided solid matter. I ob- 
served that the tadpoles did not come 
to the surface of the water to breathe, 
but continued sitting at the bottom ; 
and that the respiratory movements 
aa of the sides of the head were still 
roceeding in regular rhythm, but now were confined 
) the region posterior to the gape of the mouth, whereas 
ior to the ap ance of the front legs the move- 
ents extended up to the extreme anterior end. 
oser attention enabled me to detect minute solid 
ticles occasionally entering the nostrils, and two 
fly steady currents of water issuing from the 
bosterior end of the head, one in front of the left 
and the other in front of the right leg. 
in ase few specimens I found a crescentic, 
ened lip bounding the anterior margin 
: of these opercular openings, and was able to 
ft the flaps and pass bristles in at each, and out 
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151 
through the mouth, and conversely. This condition 
Losey until the absorption of the tail was com- 
pleted. 
Fearing that I might have encountered an abnormal 
family of tadpoles—they were rather unusually late 
in the season—I examined preserved specimens of 
which I have scores, collected years ago, in my 
laboratory for teaching purposes, and found exactly 
the same state of affairs in every one at this stage of 
development. 
To make assurance doubly sure I had vertical 
longitudinal series of sections cut through four speci- 
mens ; and these fully confirm the naked-eye observa- 
tions. 
I have little doubt that others have noticed the 
thickened crescentic lips of the two ager aper- 
tures ; for in a figure denen by Milnes Marshall, 
and in another by Howes (‘‘ Atlas of Practical 
Elementary Zoology,”’ 1902 ed., Pl. ix. Fig. xiv.) it 
is indicated. Probably it has hitherto been mistaken 
for a line of fusion between the body wall and the 
remnant of the operculum left after the front legs 
have penetrated it. Oswatp H. LATTER. 
Charterhouse, Godalming, 
January 12. 

Smell and Specific Gravity. 
In the course of some other experiments which are 
being undertaken in the Psychology Department .of 
the University of Edinburgh, a number of subjects 
were requested to arrange in serial order, accord- 
ing to smell, phials containing oil of cedar (C), 
origanum (QO), sandalwood (5), and terebene (T). 
Twenty-two experiments were made in all, and tend 
to confirm the observations made by Haycraft, Cohn, 
Zwaardemaker, Heyninx, and others, with regard to 
odour and chemical constitution. 
The serial arrangement was made, not according to 
the affect (pleasantness or unpleasantness) nor to the 
intensity, but according to * pitch,’”’ or “‘ heaviness 
and lightness,’ ‘‘dulness and sharpness ” of the 
sensation, The number of votes cast for the position 
of each substance in the series was as follows :— 
: 2 3 4 
Ss 16 4 I I 
C 4 II 4 3 
O 2 6 10 4 
ff I Y 14 
A serial arrangement according to specific gravity 
is thus represented by the voting: sp. g. S =0-974- 
0-980, C =0:939-0'96, O =0-890-0'90, and T =0-862- 
0-868. In nine out of twenty-two experiments the 
series was arranged without any error. The number 
of cases in which three of the oie were placed cor- 
rectly was as follows : SCO 10, COT 9, SCT 14, SOT 15, 
SC and OT were correctly placed relatively to each 
other in 17 instances, CO in 14, SO and CT 10, and 
ST (the two extremes) in 21 out of the 22 experiments. 
The serial arrangement as recorded above is there- 
fore by no means entirely due to chance, and the 
number of errors made diminishes the greater the 
difference between the mises gravities of the sub- 
stances employed. As the above substances of the 
terpene group are not compounds but complex 
mixtures, moreover, as the subjects without any 
further explanation were only instructed to smell 
and arrange them in a series, the results are sufficiently 
striking. J. H. KENNETH. 
Edinburgh University, 
January 10. 
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