8 OUR INSECT FRIENDS AND FOES 



of lips or lobes. Lastly, amongst the Butter- 

 flies and Moths (Lepidoptera) the mandibles are 

 aborted in the adult insect, while the maxillae 

 become elongated half-tubes, which when brought 

 together, form a long tube, provided at its ex- 

 tremity with minute hooks or spines for ruptur- 

 ing the nectaries of flowers, and when not in use 

 lies coiled in a spiral under the head. 



The large, prominent compound eyes, situated 

 on the sides of the head, are the most highly 

 developed organs of special sense possessed by 

 insects. The whole surface is composed of a 

 great number of minute hexagonal facets, closely 

 united together. Each facet is a perfectly trans- 

 parent bi-convex lens, and under each facet is a 

 crystalline cone, surrounded by pigment cells. 

 The cones are connected to the basal membrane 

 by a series of delicate rods, and round these, 

 united together, are the retinulae. The hexagonal 

 facets vary in number in different species of 

 insects, a species of Dragon-fly being said to 

 have some twenty thousand facets in its eye, 

 while a small Bee-parasite has but fifteen. In 

 addition to these'wonderful compound eyes, most 

 insects have small, simple, unfaceted eyes upon 

 the vertex or crown of their head, and which 

 are called ocelli. A great deal of very interesting 

 experimental work and observation has been 

 carried out concerning the vision of insects. In 

 connection with this work/ Lord Avebury's name 

 will be ever intimately associated, for he dis- 

 covered and demonstrated the curious fact that 

 Ants can perceive those ultra-violet rays of the 

 solar spectrum which are quite invisible to us. 



