40 
MEMOIR OF JOHN HUNTER. 
with anotlier : this union forms in some only one ca- 
nal, as in the cod, salmon, ling, &c., and in others a 
tolerably large cavity, as in the ray kind. In the 
jack, there is an oblong bag, or blind process, which 
is an addition to these canals, and communicates 
with them at their union. In the cod, &c. this union 
of three tubes stands upon an oval cavity; and in 
the jack there are two : the additional cavities in 
these fishes appearing to answer the same purpose 
with the cavity observed in the ray, or cartilaginous 
fishes. 
“ ] will here mention an experiment, to shew that 
sounds affect fishes very much, and is one of their 
guards, as it is in other animals. In the year 1762, 
when I was in Portugal, I observed in a nobleman’s 
garden, near Lisbon, a small fish-pond, full of diffe- 
rent kinds of fish. The bottom was level with the 
ground, the pond having been made by forming a 
bank all I'ound, and it had a shrubbery close to it. 
Whilst I lay on the bank, observing the fish swim- 
ming about, I desired a gentleman who was with me 
to fire a loaded gun from behind the shrubbery, 
fhe reason for desiring him to go behind the shrubs 
was, that there might not be the least reflection of 
light. The moment the report was made, the fish 
seemed to be all of one mind, for they vanished in- 
stantaneously, I'aising a cloud of mud from the bot- 
tom. In about five minutes after, they began to re- 
appear, swimming about as before.” 
During Mr Hunter’s absence with the army, the 
