1340 THE STORY OF THE UNIVERSE 



of the sides, and a pointing of either extremity, 

 adapting the animals for easy progression through 

 the water. Some fishes, such as the soles, flounders, 

 plaice, etc., are named "flat fishes" from the great 

 flattening exhibited by their bodies; although, at the 

 same time, it is important to observe that these fishes 

 are simply more compressed from side to side than 

 their neighbors. Most persons, on looking at a sole 

 or flounder, are apt to think that one of the flat sur- 

 faces must represent the back, and the other the 

 under surface of the body. This idea is strengthened 

 by the fact that the so-called back surface is dark, 

 and the apparent under surface light in color, and 

 because both eyes exist on the dark-colored surface. 

 That, however, the flat surfaces arc really the sides 

 of the fish may be seen by noting that on each sur- 

 face a breast-fin is developed; these fins being placed 

 invariably one on each side of the body. And while 

 the eyes in early life are disposed one on each side of 

 the head, in the position in which eyes are naturally 

 situated, they are gradually brought round to one 

 side by the bones of the head becoming curiously 

 twisted in the course of development. Thus these 

 fishes lie and swim on one side that which is light- 

 colored and present a most singular combination 

 of curious and abnormal features. 



The fins of fishes constitute interesting features in 

 their structure. Almost all fishes have two sets of 

 fins those which exist in pairs and those which are 

 unpaired, and which are developed in the middle 

 line of the body. To the former class belong the two 

 pectoral or "breast-fins" and the two ventral or "belly- 



