24 THE STORY OF FISH LIFE. 



It is the long cylindrical body which lies in the 

 body cavity, immediately below the vertebral 

 column or backbone. Puncture it, and see what 

 happens ! In a moment its once glistening and 

 silvery walls collapse, and nothing but a crumpled 

 mass of skin remains. That it contained air or 

 gas, there can no longer be any doubt. The 

 changes of form and other details which concern 

 the air-bladder are many, but too technical to 

 be discussed here. We must, however, pause a 

 jnoment to notice two very interesting and very 

 important points concerning this organ. 



The first and most important of these points 

 which we will examine deals with the fact that 

 the air-bladder is intimately associated with the 

 gullet. 



If we were to watch the course of develop- 

 ment of the fish within the egg we should see 

 that at one stage of this development the gullet 

 would send up a little bud, which, growing 

 larger and larger, at last would become the air- 

 bladder. As it grew more and more towards 

 perfection, so it would gradually separate off 

 from the gullet ; at last it would remain attached 

 only by a narrow tube. This tube in many 

 fishes remains open throughout life so that air 

 can pass from the gullet to the air-bladder; in 

 some it closes up, and in others it disappears 

 altogether. In cases where the connection be- 

 tween the bladder and the gullet is lost, it 

 becomes a nice question as to the means by 

 which the gaseous fluid gets into the bladder. 

 It is supposed that the difiiculty is surmounted 

 by the bladder making its own gas. 



