1889-90.] Mr W. L. Calderwood on Dactylopterus volitans. 135 
if the wall only was stimulated, no sound was produced except when 
the current was greatly intensified. He therefore concludes that the 
sound is produced by vibrations caused by the contractions of this 
diaphragm. 
In Dactylopterus, while killing two of the four specimens ex- 
amined, sounds exactly similar to those of the gurnard were distinctly 
heard, and by holding the fish between the finger and thumb in 
the region of the swimming bladder, a distinct contraction of the 
bladder could be felt as each sound was produced. These move- 
ments and sounds were quite independent of any movements of 
the operculum or mouth. 
I examined this bladder-diaphragm in Trigla Mr undo, also in 
Trigla lyra and in Dactylopterus. In all three the sphincter is 
present. Arguing from the fact that all gurnards produce these 
sounds, and that they all have perforated diaphragms, whereas a 
perforated diaphragm is, so far as I am aware, not found in any fish 
which does not produce the sounds, I am inclined to support the 
conclusions come to by Moreau. 
The flying powers of Dactylopterus are, I find, by some called 
into question. The conservator of the Naples Zoological Station 
— where these observations were made — insisted that the fish never 
left the water. I have been unable to make any observations on 
the actual flight myself, but the literature on the subject seems to 
me to be conclusive. Mobius,* in speaking of the flight of fish, 
discusses the question as to whether Dactylopterus moves the wings. 
This he does from direct observation. 
Moseley f twice describes the flight. In the second instance, 
while collecting in a boat amongst the weed of the Sargasso Sea, he 
succeeded in capturing one or two in a hand-net. They flew, he 
says, “ at a height of about a foot above the water, for distances of 
fifteen or twenty yards.” 
Comparing Dactylopterus with the well-known flying fish 
Exoccetus, the “ wings ” are, in proportion, quite as large, in each 
case reaching, when drawn close to the side, to the base of the caudal 
fin. In the former, the first six rays are detached from the rest of 
the fin, bent downwards, and are soft at their extremities. The 
* Mobius, K., Die Bewegungen der fliegenden Fische durch die Luft. 
f Moseley, Notes by a, Naturalist on the “ Challenger pp. 562 and 571. 
