IV. INSECTA: HEX.\PODA 



417 



From the outer appearance one would conclude that these holometabolous 

 Iarv« not only lacked the wings, but that the appendages of the imago were 

 entirely absent or had an entirely different form; farther, that wings, and 

 frequently antenna;, legs, and mouth parts, come into existence at the moment 

 of pupation, and then in remarkable size and completeness. In fact, the anlagen 

 of all these structures are formed long before pupation, often at the first molt. 

 The wings of a butterfly are present in the caterpillar as small folds or processes 

 of the surface which increase in size with each molt. They are not visible 

 e.xternally because they are pushed into the body and enclosed in sacs opening 

 to the e.xterior. Such anlagen are called imaginal discs (fig. 462); with their 

 recognition the distinctions between complete and incomplete metamorphosis in 



Fig. 462. — Diagram of development of wings and legs from the imaginal discs of a 

 fly during metamorphosis (after Lang), /j, larval hypoderinis; j, imagin,al hypoder- 

 mis; /, 'w^ imaginal discs and legs and \nngs formed from them; 5, connection of discs 

 with hypodermis; x, chitinous larval skin. 



part disappear, since in the first the structures of the imago, even if in a modified 

 shape, are outlined very early. Still there remains much to be remodelled 

 during the pupal rest. The muscles must be adapted to the new locomotor 

 organs, the digestive tract to the altered food, the nervous system re-formed. 

 Since a great part of the larval structures must be broken down to afford material 

 for the reconstruction of the organs, the pulpy nature of the inside of the pupa is 

 easily understood. With a rapid degeneration of the tissues this material is so 

 homogeneous that it was formerly thought that the pupa returned to the indiffer- 

 ent condition of the egg. 



With the sexual life is connected, in termites and Hymenoptera (bees, 

 wasps, ants), a community formation or social state, consisting in the association 

 of the sexual animals ('kings' or 'drones' and 'queens'), which have only 

 reproduction as their function, with 'workers' which care for and protect the 

 young and form the complicated nests, but which, on account of their unde- 

 veloped reproductive organs, can take no part in the perpetuation of the species. 

 In the Hymenoptera these 'neuters' are rudimentary females; among the termites 

 there are rudimentary males as well (fig. 464). With the termites, wasps 

 and bees, this rudimentary character of the sexual organs appears to be the 

 result of insulficient food in the larval stages. Some think this true of the ants 

 as well; others deny it. With the ants the distinction between sexual animals 

 and workers is frequently obliterated by the presence of intermediate forms 

 ('ergatoids' and 'ergatomorphs'). But even where the distinction is the sharp- 

 est, as in bees, the workers, by proper feeding, can be made to produce eggs. 

 Not infrequently there is a polymorphism among the neuters, the most frequent 

 condition being small-headed workers and large-headed 'soldiers' (termites, 

 ants). 



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