HYMENOPTERA 231 



countries, where ants abound beyond anything that we have 

 experience of, the flowering plant and the ant sometimes co- 

 operate and help one another, the ant defending the plant from 

 mischievous insects, and the plant providing the ant either 

 with sugary food, or a place of shelter, or both. The ant- 

 shelters, developed out of the living tissues of the plant, are 

 sometimes large and complete structures well suited' to the 

 habits of the insect, and serving no other purpose than that of 

 lodging them. 



Characteristic structures of ants are the petiole or stalk of 

 the abdomen (p. 229), the elbowed antenna, the 5-jointed 

 tarsus, ending in a pair of strong claws, and the comb on the 

 fore tarsus. The comb is similar to that of bees, and is used 

 to keep the body clean. The sub-family of Myrmicidae have 

 a sting ; in other ants the sting is little developed and not 

 functional ; poison may be secreted in stingless ants, but it is 

 shot out instead of being injected into a wound. 



THE CHIEF KINDS OF INSECT-LARVJE AND PUPJE 



Insect-larvse are distinguished from worms and other non- 

 arthropod animals by their jointed thoracic legs (not always 

 present), as well as by their tracheal tubes and spiracles, 

 which are very nearly universal. Other Arthropods, which 

 may happen to resemble insect-larvae in general form, 

 differ as under: — Centipedes (Myriopoda) have many pairs 

 of jointed legs. Woo'dlice, which are terrestrial Crustacea, 

 have many pairs of jointed legs, and no tracheal tubes or 

 spiracles. Mites and ticks (Arachnida) have four pairs of 

 legs, and the head, instead of being distinct from the body, 

 as in most insect-larvse, is fused with the thorax. 



Three types of insect-larvse are readily recognised, but the 

 existence of intermediate forms renders strict definition almost 

 impossible. These three types are : — 



I. The long-legged larva, such as that of the cockroach 

 and of many predatory beetles. The head is well-developed, 

 with biting jaws, and often with long antennae. The thoracic 

 legs are long, and several-jointed. There are no pseudopods. 

 The last segment often bears a pair of long, many-jointed 

 appendages (cerci). The body is usually defended by dense 

 chitinous armour, or, at least, by dorsal plates. This larva 



