, is of later origin. There were, I believe, perfect
Insects before larvae and pupae; but, on the contrary, Nauplii and Zoeae
far earlier than perfect Prawns. In contradistinction to the INHERITED
metamorphosis of the Prawns, we may call that of the Coleoptera,
Lepidoptera, etc. an ACQUIRED metamorphosis.*
(* I will here briefly give my reasons for the opinion that the
so-called "complete metamorphosis" of Insects, in which these animals
quit the egg as grubs or caterpillars, and afterwards become quiescent
pupae incapable of feeding, was not inherited from the primitive
ancestor of all Insects, but acquired at a later period.
The order Orthoptera, including the Pseudoneuroptera (Ephemera,
Libellula, etc.) appears to approach nearest to the primitive form of
Insects. In favour of this view we have:--
1. The structure of their buccal organs, especially the formation of the
labium, "which retains, either perfectly or approximately, the original
form of a second pair of maxillae" (Gerstacker).
2. The segmentation of the abdomen; "like the labium, the abdomen also
very generally retains its original segmentation, which is shown in the
development of eleven segments" (Gerstacker). The Orthoptera with eleven
segments in the abdomen, agree perfectly in the number of their
body-segments with the Prawn-larva represented in Figure 33, or indeed,
with the higher Crustacea (Podophthalma and Edriophthalma) in general,
in which the historically youngest last thoracic segment (see page 123),
which is sometimes late-developed, or destitute of appendages, or even
deficient, is still wanting.
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