INSECT METAMORPHOSIS
is undoubtedly an advantage to a larva, especially to such species as live in narrow spaces, or that burrow into the ground or into the stems and twigs of plants; but it probably just happened that the pupal stage was first developed in an insect that had ingrowing wings.
The typical larvae are the caterpillars, the grubs, and the maggots, young insects with little or no resemblance to their parents. The larvae of some of the beetles (Fig. 137) and
Fig. 139. Springtails, members of the Order Collembola, insects perhaps directly descended from the unknown wingless ancestors of winged insects
of some members of the order Neuroptera, however, are much like the adults of their species, except for the lack of external wings and the compound eyes; and even among the typical larvae some species have more of the adult characters than others. The caterpillar (Fig. 136) or the grub of the May-beetle (Fig. 131 B), for example, both being provided with legs, have a much greater resemblance to an adult insect than has the wormlike legless grub of the wasp (Fig. 133 B) or the maggot of the fly (Fig. 182 D). Hence, we see, the degree of transformation may vary much even among insects that have a so-called "complete" metamorphosis.
There are a few insects that have no metamorphosis at all. These are wingless insects belonging to the groups known as Collembola and Thysanura (Figs. 57, 139, 140) and are probably direct descendants from the primitive wingless ancestors of the winged insects. These insects during their growth shed the skin at intervals, but they do not undergo a change of form; they illustrate the
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