486 SIR J. LUBBOCK ON THE DEVELOPMENT 
which, however, is rather a general confession of faith than an explanation of metamor. 
phoses. And this they appear to have felt themselves; for they immediately proceed to 
make a further suggestion. ‘ Yet one reason," they say, “for this conformation may 
be hazarded. A very important part assigned to insects in the economy of nature, as I 
shall hereafter show, is that of speedily removing superabundant and decaying animal 
and vegetable matter. For such agents an insatiable voracity is an indispensable quali- 
fication, and not less so unusual powers of multiplication. But these faculties are in a 
great degree incompatible; an insect occupied in the work of reproduction could not 
continue its voracious feeding. Its life, therefore, after leaving the egg, is divided into 
three stages." 
But there are some insects, as, for instance, the Aphides, which certainly are not 
among the least voracious, and which eat and breed at the same time. There are also 
many scavengers among other groups of animals, such, for instance, as the dog, the pig, 
and the vulture, which undergo no metamorphosis. 
It is certainly true that, as a general rule, growth and reproduction do not occur 
together; and it follows, almost as a necessary consequence, that in such cases the first 
must precede the second. But this has no immediate connexion with the occurrence of 
metamorphoses. The question is, not why an insect does not generally begin to breed 
until it has ceased to grow, but why, in attaining to its perfeet form, it passes through 
such remarkable changes. And in addition to this, we must consider, first, the sudden 
and apparently violent nature of these transitions, and, secondly, the immobility of the 
animal in its pupa state; for undoubtedly the quiescent and deathlike condition of the 
pupa is one of the most remarkable characteristics of insect-met phosis. 
First, then, the necessity for change depends on the fact that most insects leave the 
egg in a very early condition*. The Orthoptera, indeed, and other homomorphous insects, 
are hatehed in a more advanced form, and consequently undergo fewer subsequent 
changes than is the case with other insects. Those processes, however, of evolution 
Which take place in the egg itself attract comparatively little attention, even among 
entomologists. 
We may now pass to the second part of the subject—that is to say, the apparently 
sudden and abrupt nature of the changes which insects undergo. I say “apparently, 
because the changes in the internal organs, though rapid, are in reality gradual; and 
even as regards the external form, though the metamorphosis may take only a few 
minutes, this is but the change of outer skin—the drawing away, as it were, of the 
curtain; and the new form which then appears has been in preparation for days 9^ 
rhaps, weeks before. 
Swammerdam, indeed, supposed (and his view was adopted by Kirby and Spencet) ae 
the larva contained within itself « the germ of the future butterfly, enclosed in what 
be the case of the pupa, which is itself included in the three or more skins, one over the 
other, that will successively cover the larva.” This is entirely a mistake; but it iei 
* And this, again, is proba i Se: ient to 
» » 18 probably owing to the fact that : : nsufficient carry 
the insect to maturity. 4 " act that the amount of nourishment in the egg is i 
t Loc. cit. p. 55. 
