INSECT. 661 INSECT. When such individuals, however, are developed to meet the emergency, they are generally immature in the anterior parts of the body. The termite queen differs in one respect from any other known insect — that is, in actual growth after reaching the adult stage, this gro^vth being confined to the abdominal region of the body, and being due to the necessity for an extraordinary number of eggs. The complicated character of a termite colony is seen from the following table (from Sharp), which indicate* the numerous forms which exist in certain communities: sists of not more than 21 segments, which are usually of unequal size and shape, arranged in three usually well-defined regions — head, thorax, and abdomen. The head is small and flattened or rounded, and is composed of not less than six segments, bearing eyes and at least four pairs of appendages, namely one pair of antennx and three pairs of mouth-parts. The mandibles are one-joir.ted, without appendages. There are two pairs of maxilloe, the first pair separate, usuali.v three-lobed and with a palpus which is never more than six-jointed. The second pair unite to form the under lip and bear a pair of Forms op Tehmes LnciFUGCs (Aiter Grass!) 1. Youag, undifferentiated larvee 1. Larvjp that will not mature the sexual organs. 3. LarvsD that will the sexual organs. I 4. Reserves lor royal specimens (only pres- ent when 14, 1.5, and 11 are wanting, or when 14 and 15 are present in insufficient numbers). I I 5. Larvae of soldiers. I 7. Soldiers. 6. Larvaa workers. 8. Workers. 9. Nymphs of the first form. I I 10. Nymphs of the second form. 12. Winged insects. E 14. True royal couple. A very remarkable feature of the life of social insects is the frequent occurrence, in the colonies of almost all siieeies, of 'guests,' or inquilines. Insects of several orders live in ant colonies and symbiosis ( q.v. ) presents itself here under vari- ous aspects, among which, according to Wasmann, real hospitality (myrmetoxenie and termitoxenie) and relations of friendship (symphylie) take first rank, and as far as we can tell, are un- equaled elsewhere in the animal kingdom. Was- mann has studied more than a hundred different species of insects living in the nests of ants, and more than a hundred different species in the nests of termites, but states that J^hese form but a fraction of those hidden in the nests of tropical ants, and jealously guarded by their 'jailers.' New and interesting discoveries are constantly coming to light in the tropics. Certain of the beetles found in these nests possess certain pe- culiar tufts of hair and are licked by the hosts on account of the pleasant secretion which comes from them. Tlie peculiarly shaped antenna? of the guests indicate that they summon the ant at feeding time by flipping it with these organs. Certain rove-beetles occurring in termites' nests are fed directly by their hosts. !Many of the guests are curiously modified so as to present a striking resemblance to their hosts. With those living with blind ants the form is not modified, but the structure and the hair growths have be- come similar to those of ants. Among these guest insects (which when occurring in ants' nests are kno^vn as 'nivmiecophilous' and in termites' nests as 'termitophilous') . there are representatives of no less than 31 different fami- lies of Coleoptora. seven families of Hvmenoptera, several families of Lepidoptera, Diptera, Orthop- tera. Xeiiroptera, Pseudoneuroptera, Hemiptera, Thysanura, and there are also living as guests in these nests certain curiously modified myria- pods, scorpions, spiders, mites, and isopod crus- taceans. See iNQriLiNE; Tkrmite. STRtTTfRE OF INSECTS. The insccts are most closely related to the niyriapods and to the spi- ders and their allies (Arachnida) . The body con- 11. Reserves for royal pairs (only present when 14, 15. and 4 are wanting, or when the two latter are present in Insuffi- cient numbers). I 13. Re.>^erve royal pairs ? I 15. Substitution royal pairs. palpi never more than four-jointed. The epi- pharynx forms the roof of the mouth and bears taste organs. The hypopharynx is usually well developed, and lies on the under side of the mouth just above che labium, and receives the end of the salivary duct. There is a pair of compound eyes, and usually from two to three simple eyes (ocelli). The thorax consists of three segments. There are three pairs of legs, each foot ending in a pair of claws ; two pairs of wings, a pair to each of the two hinder thoracic segments. The wings are occasionally reduced or wanting in forms which, however, had winged ancestors. The abdomen consists at the most of from ten to twelve seg- ments, and there are no functional abdominal legs except in the Thysanura and in the larvae of Lepidoptera. The genital openings are usually single, but are paired in some orders. The digestive canal is highly differentiated in the winged orders. In lanae it is a nearly straight tube extending from one end of the body to the other. In adult insects, however, it is usually much longer than the body, and there- fore is more or less folded. It is situated below the dorsal vessel and above the ventral chain of neire-ganglia. There are three main divisions, namely the anterior, middle, and posterior. The anterior and posterior divisions are morpho- logically considered as invaginations of the ex- tremities of the skin. The oesophagus is usually narrow, dilating behind to form the crop. Some- times it dilates immediately behind the mouth, and this dilatation is known as 'pharynx.' It is followed by the 'gizzard' or proventriculus. The true stomach or chylific ventricle is always pres- ent, and is very variable in shape and size. Some- times it is coiled like an intestine, and some- times bears pouches varying in number from two to very many. The intestine varies greatly in length, being smaller anteriorly and frequently widening to form a rectum. There is sometimes a caecum and odoriferous glands. The alimentary canal has two coats of muscles, a longitudinal and transverse coal. Salivary glands are pres- ent in many insects, discharge into the mouth,
