HABITS UK A DIUDUX. 17 



tity both of water and air is absorbed by the mouth, 

 and perhaps likewise by the branchial orifices. 

 This process is effected by two methods : the air is 

 swallowed, and is then f6rced into the cavity of the 

 body, its return being prevented by a muscular con- 

 traction which is externally visible : but the water 

 enters in a gentle stream through the mouth, which 

 is kept wide open and motionless ; this latter action 

 must, therefore, depend on suction. The skin about 

 the abdomen is much looser than that on the back; 

 hence, during the inflation, the lower surface be- 

 comes far moi'e distended than the upper; and the 

 fish, in consequence, floats with its back down- 

 wards. Cuvier doubts whether the Diodon in this 

 position is able to swim ; but not only can it thus 

 move forward in a straight line, bnt it can turn 

 round to either side. This latter movement is ef- 

 fected solely by the aid of the pectoral fins ; the 

 tail being collapsed, and not used. From the body 

 being buoyed up with so much air, the branchial 

 openings are out of water, but a stream drawn in 

 by the mouth constantly flows through them. 



The fish, having remained in this distended state 

 for a short time, generally expelled the air and 

 water with considerable force from the branchial 

 apertures and mouth. It could emit, at will, a 

 certain portion of the water; and it appears, there- 

 fore, probable that this fluid is taken in partly for 

 the sake of regulating its specific gi'avity. This 

 Diodon possessed several means of defence. It 

 could give a severe bite, and could eject water from 

 its mouth to some distance, at the same time ma- 

 king a curious noise by the movement of its jaws. 

 By the inflation of its body, the paj^illce, with which 

 the skin is covered, become erect and pointed. But 

 the most curious circumstance is, that it secretes 

 from the skin of its bellv, when handled, a most 

 B 2 



