10 . INSECTS AT HOME. 



clypeus, or shield, which covers the actual mouth. Fig. b 

 fhows the under side of the head. 6aa are the eyes, 66 the 

 insertion of the antennoe. 



As reference has been made to the eyes, it must be men- 

 tioned that these organs, although apparently only two in 

 number, are in reality compoimd eyes, being made of a vast 

 number of facets gathered into two groups, one on each side of 

 the head. There is an apparent exception to this deiinition in 

 the well-known Whirligig Beetles (Gyrini), which appear to 

 have four eye-groups, two above and two below. This ex- 

 ception is, hoAvever, more apparent than real ; the eye-groups 

 being in fact only two, but each pair being crossed by a band 

 of the horny material of which the outer skeleton is composed. 

 The compound eyes can be seen to great perfection in some of 

 the butterflies ; but for this purpose, a careful manipulation of 

 the microscope is needed. 



If the reader should be disposed to prepare a portion of the 

 compound eye for the microscope, he will find that the opera- 

 tion, though a rather tedious one, will well repay him for the 

 trouble. Should he wish to do so, he can so arrange the eye 

 that some small object can be seen through it, when the effect 

 will be extraordinary, the object being apparently multiplied in 

 accordance with the number of facets in the field of the micro- 

 scope. The result is, in fact, exactly the same as that which is 

 produced by looking at any object through an ordinary multi- 

 plying glass. It is not, however, to be imagined that because 

 the compou.nd eye of the insect has so many facets, the insect 

 perceives the object multiplied in proportion to the facets ; for., 

 although the numerous facets give thQ insect an extended range 

 of vision, they convey but one image to the brain, just as the 

 duplicate eyes and ears of man convey to the mind but one 

 image and one sound. 



In addition to these compound eyes, many insects possess 

 several small simple eyes, called ocelli. They are very small, 

 and in the Beetles are two in number, and placed on the bacl 

 of the head. They can be very easily seen in some of th( 

 Hymenoptera, such as the bees and wasps. The eyes of thf 

 spider are of a similar character. 



Having examined the head, we now take the next division of 



