The compound eyes vary greatly in their size. In some insects they are placed one in each side of the head (fig. [1]); in others, as in the drone bee, they meet one another at the top of the head (fig. [3], spot marked O) and extend downwards to the mouth. In others, yet again, they may attain a huge size, and occupy even the whole front of the head, crowding over the ocelli to form a little group at the top, as in the head of a species of fly known as the Bibio (fig. [4]).
The compound eye is so delicate and wonderful, that great knowledge of anatomy or the science of optics is necessary before it can be really appreciated. Briefly, it is made up of a cluster of simple eyes, in each of which there are several parts. Beginning at the surface we have what is known as the facet, or cornea, which roughly corresponds to the surface of our own eyes. Next we meet with a clear, glassy rod, and this passes downwards into the nerve of sight. Around these rods is a sheath of black colouring matter, so that each eye is cut off from its neighbour. Thus the whole eye may be likened roughly to a bundle of telescopes.
Of what use, it may be asked, are the three little eyes in the middle of the head of insects which have these wonderfully complex eyes? Well, the large compound eyes are used to watch the movements of other animals; thus they are enabled to escape their enemies. Many of you doubtless have tried to catch butterflies, and if so you will know how suddenly and quickly they avoid the master-stroke that is to land them in the net. But the use of the three little eyes seems to be to enable their possessor to see in the dark. By their means the bee (figs. [2] and [3]) can distinguish objects even in the darkest parts of the hive; so too the ant can find his way about the galleries of his underground home. Night-flying moths all have these little eyes, whilst in butterflies, which fly in the daytime, they are wanting.
W. P. Pycraft, A.L.S., F.Z.S.
TWO WAYS OF READING A SENTENCE.
People in high stations of life often receive from authors presents of their works, and are expected to say something flattering about them in return. They do not like to hurt the author's feelings if the book is worthless, and so Benjamin Disraeli, when Prime Minister, used to answer those who approached him in this way: 'I have received your book, and shall lose no time in reading it.' This sentence, as you can see, is capable of being read in two ways, but the sender of the book was, of course, intended to understand the more flattering reading. It was a kind of deception, and was not very honest, but it was done out of kindness.
A musical composer found another way of answering the many applicants for his opinion: 'I have received your music,' he would write, 'and much like it.'
S. Clarendon.