102 MARVELS OF FISH LIFE 



through the overflow hole. I show an illustration of the 

 ditch from which the food-laden water was gathered, 

 and the box below it. Owing to the kindness of my 

 friend, Mr. Mower, who visited these fish morning and 

 evening, and cleared the box and pipes of scum, this 

 simple apparatus never failed the whole summer. 



As the water in the box was only nine inches deep 

 the eggs, larvse, and young fish could easily be watched, 

 and specimens gathered when required for photographic 

 purposes. 



Without going into minute details, which would be 

 out of place in a book of this kind, I will describe the 

 early history of the roach during the first year of its 

 life, and this may be taken as an example of the carp 

 in our ponds and rivers. Before doing so, however, it 

 is necessary to say a few words about the gas bladder of 

 fishes, for the habits of the roach before and after this 

 appears, are entirely different. Almost all bony fishes 

 possess a bladder, which runs along the body just under 

 the backbone. This bladder though commonly known 

 as an air bladder, does not contain air, but mainly 

 oxygen gas, and its presence in the body of the fish 

 makes it, bulk for bulk, the same weight as water. Thus 

 the fish floats, and having no weight to support, swims 

 with the minimum of exertion. A fish is also able to 

 diminish or increase the amount of gases in this bladder 

 so as to float in different depths of water. The gas 

 bladder of a carp has a constriction in the middle as 

 shown in the illustration on the opposite page. 



