96 FISHES DIAGRAM 5 



The skeleton of fishes in not always of the same nature. In 

 some, it is formed of hard and sharp bones : in others, on the 

 contrary, as in the ray, sturgeon and lamprey, there are no 

 bones, but only a skeleton composed of tough cartilages which 



Skeleton of Fish. 



break between the teeth. For this reason, fish are divided into 

 two large orders, that of the osseous fishes which have bones, 

 such as the salmon, herring, and pike ; and that of the carti- 

 layinous fishes, which have none. 



The habits of fish are in general very little known, and we 

 shall chiefly speak of kinds which furnish very cheap and 

 abundant food. 



If we wish to observe the habits of various small kinds of fish, 

 and in general of all water animals, we can always make a cheap 

 aquarium with a bell glass like gardeners use, by turning it up- 

 side down between the legs of a reversed stool. In order to 

 keep an aquarium, or rather to make it keep itself, in order, 

 there are several precautions to be taken. We must put at the 

 bottom some small pebbles, and a stone or two, and especially 

 some flints with a hole in them. Care must be taken to set the 

 aquarium in a place which is neither too dark nor too much ex- 

 posed to the sun. It is good to suspend in it a flower-pot with 

 an aquatic plant. Some water-lentils might also be strewn over ; 

 but it is necessary that the surface should be very little covered. 

 Lastly, it is important not to put too many animals into the 



