22 THE CLASSIFICATION OF INSECTS 



tions and extensive comparisons ; for it is not now very well nnderstood, nor is its 

 character fully and justly appreciated. 



From its appearance among Lepidoptera, it is generally represented as a dormant 

 state in the development of the young butterfly, as a sort of mummy almost without 

 life ; while, in reality, it is a period of the most extensive organic activity, during 

 which the greatest changes are going on in the structure preparatory to the ap- 

 pearance of the perfect insect. When the butterfly leaves the pupa, it undergoes 

 no further organic change ; all the changes took place chiefly during the period when 

 the caterpillar was transformed into a pupa, and during the pupa state itself This 

 stage of growth is therefore to be considered as one of the most important periods 

 in the development of the insect, just as the growth within the egg is with refer- 

 ence to the caterpillar. The homogeneous cellular mass which constitutes the egg 

 gives rise to the caterpillar ; when hatched, it is already fully developed as a cater- 

 pillar, and grows only to a larger size as such ; but its structure, as far as it is 

 characteristic of that state, is introduced during the metamorphosis of the substance 

 of the egg from which it arises, in the same manner as the perfect insect is formed 

 from the changes which the caterpillar undergoes under its last skin, and during the 

 earlier part of its pupa state. These are the two great periods of development ; the 

 other periods are periods of growth. The caterpillar feeds upon large quantities of 

 food, grows to a larger size, and stores up large quantities of organic matter, out of 

 which, by another extensive metamorphosis, the perfect insect is developed ; which, 

 when mature, lives only to reproduce its kind. Up to that period the development 

 is decidedly progressive, and up to that period we see even those articulated animals 

 which undergo a so-called retrograde development advance in their metamorphosis 

 from lower to higher structures, from a simpler to a more complex organization. 



Now, are not the insects which undergo the most extensive metamorphoses to be 

 considered as the standards from which the forms of other articulated animals have 

 to be appreciated ] Is not the fact, that caterpillars bear so close a resemblance to 

 Worms, a sufficient indication that the Worms rank lower than Insects I No serious 

 objection can be made to this principle ; and if so, may not the relative position of 

 Crustacea between Worms and Insects be determined upon the same principle '? It 

 can be shown that we have no other safe guide to determine the true relation be- 

 tween the diff"erent classes of articulated animals. 



Let us first compare, more fully, the larval condition of Insects with adult Worms. 

 And here I cannot but regret that the larvse of Insects have not all been so carefully 

 studied as those of Lepidoptera, and more minutely described and figured than they 

 are in our entomological works ; for, generally, all that is given there has mere 

 reference to their general form, and even the external parts are not always described 

 and figured with sufficient accuracy. It seems as if a knowledge of the external 

 forms only were to be acquired ; and as if the morphology and structure of the parts 

 in their successive changes were of no consequence to the appreciation of the aflan- 

 ity of animals before they have attained their final development. However, we find 

 among Insects larvae entirely destitute of external appendages, the body consisting 

 of several uniform joints, and the head being scarcely distinct from the other articu- 



