OF CHLOËON (EPHEMERA) DIMIDIATUM. 485 
banded with ochre; filaments very long and white, remotely dotted with black; legs 
straw-colour; nervures of wings very faint."— Phil. Mag. 1834, p. 121. 
Having thus traced up, step by step, the history of this insect from a period when it 
is no more than yg of an inch in length until its appearance in the perfect state, I will, 
in conclusion, say a few words on the general subject of insect-metamorphoses. The two 
points to which I would particularly call the attention of entomologists are :— 
First, the gradual changes which are undergone by these larve. We shall, I believe, 
find the same to be the case with other larvæ of the homomorphous series of insects. 
And, secondly, the fact that many of these changes bear no reference to the ultimate 
form of the insect, but are connected with the conditions in which the larva itself is placed. 
Moreover I have called attention to the fact that there are certain differences even 
between the proimago and the imago. These, indeed, are not extensive; the mere 
presence or absenee of minute hairs on the surface of the wing, and of a fringe on its 
posterior margin, may not seem in themselves at first sight to be points of much interest 
or importance; when, however, they are taken in conjunction with the changes which 
occur in the antennæ, with the formation and subsequent disappearance of the branchiæ 
and middle tail, as well as with other similar facts which have been recorded in this 
memoir, they appear to suggest considerations of much interest. 
e larve of insects are generally regarded as being nothing more than immature 
states, as stages in the development of the egg into the imago; and this might more 
especially appear to be the case with those insects in which the larve offer a general 
resemblance in form and structure (excepting of course so far as relates to the wings) 
to the perfect insects. Nevertheless we see that this would be a very incomplete view of 
the case. The larva and pupa undergo changes which have no relation to the form which 
they will ultimately assume. With a general tendency, as regards size and the produc- 
tion of wings, to this goal, there are combined other changes bearing reference only to 
their existing wants and condition. 
Nor is there in this, I think, anything which need surprise us. External circumstances 
act on the insect in its preparatory states as well as in its perfect condition. Those who 
believe that animals are susceptible of great, though gradual, change through the influence 
of external conditions, whether acting, as Mr. Darwin has suggested, through natural selec- 
tion, or in any other manner, will see no reason why these changes should be confined to 
» mature animal. And it is evident that creatures which, like the majority of insects, 
> during different periods of their existence in very different circumstances, may ged 
*80 considerable changes in their larval organization, in consequence of forces "nos 
^ their larval condition, not, indeed, without affecting, but certainly without affecting to 
” corresponding extent, their ultimate form. ue 
in itg in this manner, I think, understand those cases in which animals, very similar 
E mature condition, are very unlike in their earlier stages. eds 
© Question still arises, Why do insects pass through metamorphoses? Messrs. Kirby 
nd Spence tell us that they “can only answer that such is the will of the Creator ” *,— 
* * An Int i tomology,’ sixth edition, vol. i. p. 61. 
VOL, n Introduction to Entomology. 8x 
