We must guard our definition of what a pupa is, by reminding the reader that some insects with which he is very familiar do not pass through this change in the same manner that the majority of insects do; that is, in a state of torpor or sleep. If he were to rear up a spider from the egg, and were to watch for the time when it would become a still, lifeless-looking object, like that which we have called a pupa, he would assuredly be disappointed, and he might accuse this little work of leading him into error, because it declares that all insects must pass through the pupa state before they become perfect in their form and number of their parts. Yet that very spider has passed through both the larva and the pupa state under the observer's eye without his being able to recognise the fact, simply because in both these states it is very like the perfect insect, and can walk about and eat just as usual. In fact, it is more than probable that spiders of the same kind in these different conditions could scarcely be recognised so as to say that they were pupæ, or perfect insects, even by tolerable entomologists; and it is very likely that mistakes of this kind have often occurred.[I] We learn, therefore, from this statement, that some pupæ are active, and move about just as they did before, although they _are_ in the pupa state. In a great number of cases, then, a pupa is a state in an insect's life when it rests from active exertion, and from taking food, and when, underneath the dry and withered skin, a series of great changes are taking place, which are preparing it for its future life in the perfect state. Thus it differs from the _larva_ state in not eating and moving, and in the important particular,--that it is receiving new parts and organs, which are added to it under the skin. It also differs from the _perfect insect_ in the same respects as in the first place from the larva, and also in the important circumstance, that the perfect insect the moment it enters that state, has no more organs added to it--it is, in fact, perfect, while the pupa is imperfect. Let us place these differences in a tabular form:-- The Larva The Pupa The Perfect Insect Moves about and eats. Does not move about Moves about and eats. nor eat. Has no new organs Has no new organs added to it beyond Has several new organs added to it, beyond those acquired in the added to it, to prepare those obtained in egg. it for the perfect state. the pupa state.