The childhood of animals / by Sir P. Chalmers Mitchell.

  • Peter Chalmers Mitchell
Date:
[1940]
Catalogue details

Licence: In copyright

Credit: The childhood of animals / by Sir P. Chalmers Mitchell. Source: Wellcome Collection.

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    related, and they do no more than give an idea how the extremely different modes in which modern insects develop show a trace here and a trace there of different parts of a common ancestral history, some parts of which have been blurred and condensed in some insects, other parts in others. The delicate and transparent pupal skins surrounding the fly inside its puparium, with their rudimentary wings, and the pupal cases themselves of moths and oil-beetles with their rudimentary wings, plainly represent the active later larval stages of the locust. The campodeiform larvae of the oil- beetle and of many other beetles, cockroaches and earwigs represent the primitive insect, and may pass by a series of moults into the adult, or these later stages may have been condensed to a sudden metamorphosis. The caterpillar-like larva is a rather degenerate modification of the Campodea larva, and the maggot-like larvae of many beetles and the legless larv^ of flies are still more degenerate interpolations in the life-history, fitting the special conditions in which these larvae live. The stories of the youthful period in the crustaceans and insects are, to a certain extent, alike. The hard nature of the skin has led to a replacement of the more usual method of continuous growth, by growth in little jumps, there being a moult at each jump. In both there are many animals in which these successive moults separate a set of laroe which are becoming more and more like the adult by slow stages. In both the more continuous sets of larvae seem to be at least a partial repetition of the ancestral history, but in both the larva are modified in many Ways to suit the needs of their own life, and it is a difficult judgment to decide in any case how much of the character of a larva is adaptive and how much ancestral. In both groups the continuous series may be interrupted at any point by the obliteration or telescoping of some of the stages, with the result that occasionally a moult is preceded by a resting phase in which the larva is more or less torpid and motionless, and when the form that emerges from the moult is widely different from the preceding form. Such bigger jumps give rise to the familiar metamor* phoses, and they are most frequent and most decided when
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