668 
NATURE 
[May 19, 1923 

The Adhesive Apparatus of the ‘‘ Sucking-fish.’’ 
Ir is regarded in text-books * as a well-established 
fact that the adhesive organ of the “ sucking-fish ”’ 
(Echeneis and Remora, etc.), and a somewhat 
similar structure in Pseudecheneis and certain other 
freshwater fish, functions as a “‘sucker’’; in other 
words, it enables the fish to adhere by the creation of 
a vacuum, or at any rate a partial vacuum, between 
the ridges and the rim of which it is consti- 
tuted. Observations on Pseudecheneis and its allies 
in natural conditions led both Dr. Annandale 
and myself to doubt whether this belief is well 
founded. : 
It is very significant that, as several observers have 
noted, Echeneis can be detached from its hold quite 
easily by either thrusting it forwards or sideways,’ 
while the so-called rim of its adhesive apparatus is 
entirely absent as a raised ridge in fresh material or 
well-preserved specimens. The whole structure,® 
moreover, differs in almost every respect from the 
true sucking disc present on the lower surface of 
the fish Garra * (Discognathus) and of the tadpoles ° 
of Rane Formose. 
I have recently had an opportunity of conducting 
experiments on the living Pseudecheneis, and have 
also had the great advantage of being able to consult 
Proi. C. V. Raman on the physics of adhesion 
both in this genus and the true Echeneis. We are 
convinced that the apparatus of these species, unlike 
that of Garra and the tadpoles mentioned above, is 
not a true sucker but essentially an elaborate device 
for producing the maximum amount of friction. It 
is correlated in a very interesting way with the shape 
of the fish. The upper surface of Echeneis and the 
under surface of Pseudecheneis are flattened to 
increase frictional area, while the lower surface of 
the former and the upper surface of the latter have 
adopted such a form that an advantage is taken of 
the swift current, which, instead of dislodging the 
animal, presses it against the substratum. The 
pressure exerted by the current increases friction, 
for friction is proportional to two factors—the co- 
efficient of friction and pressure. The coefficient of 
friction is increased by the presence of a large number 
of strong spines, all of which are directed backwards 
on the lamelle of the pad of Echeneis, and by in- 
numerable microscopic epidermal spines * found on 
the ridges of the adhesive discs of hill-stream fishes. 
The plates bearing the spines in Echeneis point 
posteriorly, with the result that the spines come into 
action against the opposing surface when the fish 
is pressed backwards by the current, but are released 
when the movement is in the opposite direction. 
The enormous difference in the frictional coefficient 
for forward and backward movement is easily noticed’ 
when a finger is passed over the pad of a preserved 
specimen of Echeneis. It is also possible that the 
ridges and grooves in these fishes assist in increasing 
friction much in the same way as the ridge- and 
groove-patterns to be found on the tyres of motor 
cars. 
Echeneis can cling to smooth surfaces in the 
absence of currents.? The strong spines on the 
lamelle are quite sufficient to render this possible, 
and the phenomenon is not at first sight so remarkable 
1 Giinther, ‘An Introduction to the Study of Fishes,” pp. 460 (Edin- 
burgh: 1880); Dahlgren and Kepner, ‘“ Principles of Animal Histology,’ 
pp. 414 (New York: 1908). 
2 Holmwood, Proc. Zool. Soc. London, pp. 411 (1884); Gudyer, Ann. 
Mag. Nat. Hist. (9), I1., pp. 271-306 (1918). 
2 Storms, Ann. Mag. Nat. Hist. (6), I1., pp. 67-76 (1888). 
* Hora, Rec. Ind, Mus. XXIV., p. 47 (1922). . 
® Annandale and Hora, Rec. Ind. Mus. XXIV., pp. 505-509 (1922). 
® Hora, Rec. Ind. Mus. XXIV., pp. 47-58 (1922). 
? Hornell, Madras Fisheries Bull., X1V., pp. 66 (1927). 
NO. 2794, VOL. IIT] 



as the power of adhesion in opposition, as it seems, 
to a strong current. 
This note is written chiefly with the object of 
bringing this new view of the mechanism of the 
so-called sucker to the notice of other workers, 
particularly of those who are in a position to make 
observations on living specimens of Echeneis, Remora, 
etc. I hope myself shortly to undertake fuller 
studies of the morphology and histology of the 
adhesive pad with the view of elucidating the subject 
further. SuNnDER Lat Hora. 
Indian Museum, Calcutta, March 29. 

Vertical Change of Wind and Tropical Cyclones. 
In his article on the birth and death of cyclones 
(London Meteorological Office, Geophysical Memoirs, 
No. 19, 1922) Sir Napier Shaw makes the interestin, 
suggestion that the shearing of the head of a tropi 
cyclone with reference to its foot, by difference of 
velocity at different levels in the air which carries 
it, might cause its dissolution. If the hypothesis 
that the movement of a cyclone is due to its being 
embedded in a flowing current of air is correct, it 
will of course be admitted that if there is a con- 
siderable gradient of wind upwards, positive or 
negative, then there must be a continual shearing of 
the cyclone and the shearing must either be continually 
countered by the cyclone, or it must die. But the 
question is, whether there are occasions when a cyclone 
has to face such a strong vertical gradient of wind, 
and if there are, what vertical gradient a cyclone can 
stand and continue to live? With regard to the 
first point, from an examination of the symmetry of 
temperature and pressure Sir Napier Shaw remarks : 
‘“If isobaric surfaces are also isothermal surfaces 
there is no change of wind velocity with height. In 
any case one would have to assume approximate 
uniformity of direction and speed for a thickness of — 
several kilometres, in order to get a definite connected 
body of air in stable motion. Perhaps for the levels 
between four and eight kilometres there are enough 
occasions of little change of wind velocity between 
those levels to furnish convenient circumstances for 
the persistence of a sufficient number of cyclones *or 
cyclonic depressions.” ' ; 
The atmospheric conditions in the region sur- 
rounding a cyclonic depression are so different from 
those of normal weather, that it is perhaps quite 
incorrect to assume that the vertical gradient of 
wind, which a cyclone has to encounter, is roughly 
of the same order as the gradient derived from the 
observations of the motion of pilot balloons under 
normal conditions. As pointed out by Sir Napier 
Shaw, it is also a matter for careful considera- 
tion, what is actually presented to us by the motion 
of a pilot balloon in a cyclonic depression. The 
irregularities due to local turbulence or the changes 
incidental to an inclined axis will appear in the 
results with as much weight as the examples of 
fundamental structure. Perhaps the altered condi- 
tion of the atmosphere in which a fully developed 
cyclone finds itself does not permit of too much change 
of wind velocity with height, and then all our con- 
jectures regarding the supposed effect of a Vertical 
gradient of wind on a cyclonic system will appear 
futile. 
If a cyclone is to be considered a stable dynamical 
system consisting of a vortex with a ring of maximum 
velocity, as Sir Napier Shaw considers it to be, and 
“ protected from the ordinary vicissitudes of weather 
by the enormous momentum of a vortex with a high 
rate of spin,’”’ then as a vortex will generally, except 
perhaps for the fact that air is not a perfect fluid, 

