70 OUT OF DOORS. 



violently with both swimming-feet at the same moment, 

 and thus jerking themselves several inches into the air. 

 Almost simultaneously with the spring, they spread their 

 wide wings, and flew off with incredible speed. 



There is an old fairy tale about three sisters, who 

 had respectively one, two, and three eyes, the elder and 

 the youngest treating their sister very contemptuously 

 because she had two eyes like people in general. Now, 

 a whirlwig beetle goes one step beyond them for it has 

 four eyes, two above and two below two to see below 

 the water and two to see above it. Of course the beetle 

 has in reality a vast number of eyes, like most insects, 

 but those eyes are divided into four masses instead of 

 two. The reason is this. The insect is continually 

 scurrying about on the surface of the water, watching 

 for prey, and if its eyes were constructed in the ordinary 

 fashion it would only be able to see either above or below 

 the surface, according as its eyes happened to be placed. 

 In order to be able to see distinctly any object below 

 the surface of the water, its eyes must be submerged ; 

 and in the eyes of this little beetle we find the principle 

 of that well-known instrument, the water telescope. 

 This is used for the purpose of looking into the water, 

 and is simply a tube with a plain glass fixed water- 

 tight into one end. When the glass is pushed under 

 the surface of the water, and the eye applied to the upper 

 part of the instrument, objects can be seen with great 

 plainness, the vision not being obstructed by any ripples 

 on the surface of the water. 



