no ANIMAL LIFE UNDER WATER 



bones are triturated away, while the denser bone 

 round an air space on each side of the skull 

 remains. 



An air space on either side of the skull, 

 surrounded by dense bone, suggested some 

 arrangement in connection with the sense of 

 hearing. I therefore sent some vesicles, with 

 notes, to Professor Herdman, and received the 

 following answer : "Dr. Johnstone has just dis- 

 sected out the head of a sprat, and finds that 

 the vesicles are the anterior end of an extension 

 of the air bladder to the skull; they are what 

 are known as ' the anterior air vesicles,' and 

 were described by Duncan Matthews in the 

 Scotch Fishery Board Report, Vol. V., in the 

 'eighties." 



To the reader who is not conversant with fish 

 anatomy, I would explain that in most bony 

 fishes there is a swim bladder under the backbone, 

 which is filled with gas. In the herring family 

 a fine, tube-like prolongation extends from this 

 bladder to the air space described. Vibrations 

 in the water which reach the sides of the fish 

 affect the swim bladder, and are conveyed by 

 this extension to the air vesicles. As these air 

 vesicles are in the region of the brain, the vibra- 



