ON THE FLIGHT OF THE FLYING-FISH. 477 
“Flapping movements of the large shining pectorals would 
make themselves visible by the alternate appearance and disap- 
pearance of the light reflected from them. They would escape 
no accurate observer who viewed the fully-expanded pectorals 
from the height of a steamer. But as often and as long as I have 
been able to follow, with my eyes, Flying-fish, which came out of 
the water near our boat, I have never seen light reflected in this 
manner from the pectoral fins as from the wings of birds and 
bats” (p. 353). 
That these movements have escaped Prof. Mobius is then 
evident from his own testimony: what application then is to be 
made of the statement that ‘‘ they would escape no accurate 
observer ?”’ This author first attempts to account for the fact 
that many good observers have affirmed the wing-like movement 
of the fins on historical and psycological grounds, asserting that 
this ‘‘ false notion” had its origin in a fancied resemblance of 
these fishes to swallows, and that it has been handed down from 
the times of Aristotle and Pliny to the present time simply 
on authority; and afterwards, as if aware that this was not 
altogether a satisfactory solution of the question, admits that 
these observers may have had some grounds for their statements, 
but thinks they were deceived by appearances, which they did not 
understand, into the belief that the fins behave like wings. He 
is very frank in telling us just what these appearances are, 
although no one, not even Mobius himself, has ever observed 
such phenomena in a living Exocetus. 
*‘ Just as a sail begins to slacken and vibrate the moment the 
wind blows parallel to its surface, so the more flexible and elastic 
distal and ventral parts of the pectoral fins are thrown into rapid 
vibrations when the air-current moves parallel to their surface ” 
(p. 370). 
As a simile, this will do very well, but how is it as a matter of 
fact? We are assured that this comparison is fully justified by 
the following simple experiment :—A specimen of Exocetus, 
shrivelled, distorted, and stiffened by long soaking in alcohol, was 
suspended, and its pectorals exposed to a swift current of air in 
such a manner that the current swept along both surfaces. The 
fins thus exposed “‘ made directly under my eyes the same rapid 
quivering movement that various good observers of Flying-fish 
have regarded as a flying movement” (p. 870, 871). It is im- 
