EYES IN THE BACK OF THEIR HEADS.

Bruce Herald, Volume XXX, Issue 3030, 24 January 1899, Page 3

EYES IN THE BACK OF THEIR HEADS.

To say that a person " has eyes in the back of his head " has lone been a recognised way of paying a high compliment to his powers of observing everything going on arouud him. But the phrase when applied to insects becomes, as naturalists are well aware, simply a statement of fact. Indeed, considering that very many insects .indulge in eyes by the thousands, the head of a horsefly, for example, being literally made up of eyes alone, it would be strange if ; some of them had not to be relegated to the j back of their owners' lieads. j Thus it is said that if an ordinary dr gon fly were placed in the centre of a globe he . could see every part of it at once without « moving his head. j And thiß insect, though possessing about ' 20,000 eyes, is a long way from being the most liberally endowed in this respect, the mordella beetle, for instance, comfortably i beating him by some 5,000. These eyes often give off prismatic colours, and under the microscope are very beautiful objects, looking like a section of honeycomb. That each individual eye of the many thousand has its perfect lens system is proved by the fact that each makes a separate picture of 'any object placed before it. j 'Of course, a microscope is required to see ' pictures, but they are very distinct and are known to microscopists as the " mul- , ti'p]e image." | i