316 TH^ ANIMAL KINGDOM 



group includes many orders, such as the Orthoptera (grasshoppers, 

 crickets, mantids and roaches), Isoptera (termites) and Hemiptera (the 

 true bugs). Representatives are shown in Figure 16.25. The Endop- 

 terygota are the so-called "higher" insects. The young have internal 

 wing buds that later evert suddenly in a resting stage, the pupa (Fig. 

 16.24), and become full-sized wings on the following molt. This is asso- 

 ciated with marked changes in appearance, so that the young seldom 

 resemble the adults. Such development is called complete metamorpho- 

 sis and the young are called larvae. The Endopterygota also includes 

 many orders (Fig. 16.26) such as the Lepidoptera (butterflies and moths), 

 Coleoptera (beetles), Hymenoptera (bees, ants, wasps), and the Diptera 

 (flies, mosquitoes). Most of the species of insects are included in these 

 four orders, which are further described with the illustrations. Although 

 the butterflies and some moths cannot fold the wings flat upon the 

 body, the wing articulations and muscles indicate that this represents an 

 evolutionary loss, and that these insects are properly grouped with the 

 Neoptera. 



144. Metamorphosis 



A change in the shape or relative size of body parts during growth 

 is called metamorphosis. In organisms such as man and other mammals 

 the young resemble adults and little metamorphosis takes place. In other 

 organisms metamorphosis may be marked. We have already described a 

 number of examples, such as the coelenterate polyp and medusa, and 

 the larval and adult tapeworms, flukes, molluscs and annelids. 



The apterygote insects show very little metamorphosis. Young hatch 

 as miniatures of their parents, easily recognizable as to species. In the 

 living Paleoptera the young are aquatic and often have a very different 

 appearance from their parents (Fig. 16.23). They not only lack wings, 

 but have a different body shape so that the species cannot be identified 

 unless they are reared to maturity. Although the young differ from the 

 adults, their bodies are complete with jointed legs and compound eyes. 

 Metamorphosis in the Exopterygota is similar, except that since both 

 young and adults are terrestrial, they do not differ so much in appear- 

 ance. Young grasshoppers, for example, are easily recognized as grass- 

 hoppers. 



In the Endopterygota the young not only show little resemblance to 

 the adults, but often lack such structures as compound eyes, jointed legs, 

 and wings. Some larvae have no appendages at all. As the larva grows, 

 wing buds develop inside the body, but are not evident externally. 

 Finally, in a single molt the appearance changes markedly as the animal 

 pupates. The pupa is a nonfeeding stage (Fig. 16.24) in which all of the 

 adult appendages are visible as external buds. Internally, whole organ 

 systems may be dissolved and replaced as the adult form is developed. 

 The pupa molts to become a full-grown adult. 



Metamorphosis is considered to involve the same phenomena that 

 appear in the formation and development of embryos. Gastrulation, the 

 formation of limbs and development of organ systems in the embryo are 



