III. The insect, No. 3, is a pupa called the _Incomplete_. It is _inactive_, but possesses rudiments of legs and wings. The common wasp is represented as an example of this kind.
IV. The insect, No. 4, is a pupa called the _Obtected_.[K] This pupa has its upper portion encased in the peculiar manner represented, the chest and lower portion being distinct. The butterfly pupa belongs to this division.
V. The insect, No. 5, is a pupa called the _Coarctate_.[L] In this case the pupa is enclosed within its larva skin, which forms a globular or oval case, the pupa lying loosely in it as if it had shrunk to a smaller size. The pupa of the blow-fly is an example.
Such are the five variations of pupæ, as they were recognised by Linnæus--the _Complete_, _Half-complete_, _Incomplete_, _Obtected_, and _Coarctate_. They are sufficiently minute for ordinary purposes: and it will possibly save the reader some confusion of ideas to endeavour to fix them in the memory; so that when looking at an insect whose pupa state may not be so very characteristic as that of the blow-fly, or butterfly, he may still be able to say with confidence, that although it is unlike these, it is nevertheless a pupa. On all subjects nothing is of so much importance as clearness of ideas. It is better to know only a few things, and to understand them clearly, than to have a confused and indistinct knowledge of a great number. It has been, therefore, simply and entirely with a view to obviate this state of things in the mind, that these definitions of the different kinds of pupæ, which may have appeared not altogether interesting, have been given.
Having fulfilled this duty, we may now proceed to the more agreeable task of ascertaining some interesting facts relative to the insect's life and age in the pupa state. We have already seen that the insect in the larva state often arrives at a very respectable old age; indeed, in this state insects live longer than either in the pupa or perfect states. But pupæ also attain to a very fair number of days, sometimes living as long as two years in that state. Often, however, they are not more than a few days in this condition, and the insect, after a short repose, springs forth a new and active being. But it has been found that insects live a longer or shorter period in the pupa state according as the temperature of the air is cold or hot. Thus, for example, when the larva of a moth has become a pupa in the early part of summer, the pupa state will generally not last beyond a fortnight. But if, on the other hand, the larva becomes a pupa late in the autumn, the pupa state will last until June in the next year: thus manifestly teaching us that according as the weather is mild and genial the pupa state will be shortened; or according as it is cold and rigorous it will be increased in duration. The ingenious Réaumur determined to put these singular facts to an experimental test; and as his results are in the highest degree interesting and important, we shall proceed to submit an abstract of them to the reader's notice.