136 
Proceedings of Royal Society of Edinburgh. [sess. 
pectoral muscles are powerful. They are arranged in a superficial 
and a deep layer, both above and below the fin, and are in pairs. 
In the upper pair, the superficial elevates, and at the same time 
protracts ; the deep adducts, sweeping the fin in to the fiank. The 
fin rays are devaricated from one another by tendinous fibres 
passing across the upper surface obliquely from the anterior portion 
of the superficial protractor. The detached portion of the fin is only 
very slightly acted upon by fibres from above. 
In the lower pair, both divisions of the fin are drawn forwards 
and downwards by fibres from both muscles, the superficial, however, 
which is coarsely fasciculated, having the stronger action upon the 
large portion of the fin. The detached portion, indeed, has an ex- 
tremely limited motion, and always must stand out at an angle from 
the body of the fish. The swimming bladder of Exocoetus occupies 
the ordinary position in the abdominal cavity and is non-muscular. 
This fish, I have no doubt, is capable of flying a much greater 
distance than Dactylopterus ; it has much less mass, and in form is 
calculated to offer much less resistance to the air, and more readily 
to retain its natural position, when out of the water, owing to 
its deep-keeled herring body. The significance of the peculiar 
swimming bladder in Dactylopterus now seems to me to be 
explained. 
The true gurnards, that is, the near allies of the Cataphracti, are in 
habit bottom feeders. The tips of the free fin rays are provided 
with isolated sensory elements,* causing these portions to have a 
function analogous to the antennse of crustaceans. Their swimming 
bladders have no pneumatic duct and no muscle. When brought 
suddenly to the surface by means of a net or line, Trigla invariably 
floats belly up. If the fish is then opened, the bladder is found to 
be violently expanded. The expansion naturally takes place in a 
downward direction amongst the abdominal viscera, this being the 
line of least resistance. The balance is in this way destroyed beyond 
recovery, and the position of the fish is reversed. I have kept Trigla 
cataphmda in a tank in this condition for two days. The fish 
eventually dies. The reason of the expansion appears to me to be the 
sudden removal of pressure consequent upon the fish being brought 
* Zincone, A. 
pesci, 1876. 
Osservazioni anatomiche su di alcune appendici tattili dei 
