INSECTA. 



879 



in the females of this class, a circumstance 

 to which we shall return in our description 

 of the skeleton of the perfect insect. 



The Pupa. We have seen that after leaving 

 the larva or feeding condition, the insect as- 

 sumes one of a very different form, which is 

 called the pupa, nymph, aurelia, or chrysalis 

 state. The two latter terms were applied by 

 the older entomologists to this stage of transfor- 

 mation in butterflies and moths. The term aure- 

 lia was used, as expressive of the beautiful gol- 

 den colours or spots with which many species are 

 adorned, as Vanessa urticte, v. atalanta, and 

 others. The term chrysalis had a similar sig- 

 nification. Linnaeus, desirous of employing a 

 term that would be applicable to this stage of 

 transformation in all insects, adopted that of 

 pupa, because in a large majority of the class 

 the insect is as it were swathed (Jig. 367) 'or 



Fig. 367. 



Pupa of DeHephila Elpenor. ElepJiant hawk^moth. 



bound up, as was formerly the practice of 

 swathing children. This kind of pupa, in 

 which the future limbs are seen on the out- 

 side of the case, is called obtected. The term 

 nymph, which is sometimes employed, is 

 applicable only to those species in which the 

 limbs remain free, but are folded up, as in 

 the pupae of the butterfly and moth, and are 

 not covered with a hard uniform case; as in 

 many Coleopterous and most Hymenopterous 

 insects (Jig. 368). When the pupa is in- 



Fig. 368. 



Nymph or pupa state of Vespa crabo. 

 Magnified. 



Hornet. 



closed in a smooth uniform case, but no signs 

 of the limbs or other parts of the body are 

 visible, as in Diptera, it is called coarctate. 

 In these insects the skin of the larva is not 

 cast off at the period of changing, but becomes 

 the covering or coccoon of the included pupa, 

 which is also inclosed in its own proper skin 

 within it. In all insects which undergo a com- 

 plete metamorphosis, this is the period of quies- 

 cence and entire abstinence. Many species 

 remain in this state during the greatest part 

 of their existence, particularly the true pupae 

 of moths and sphinges, which often continue 

 in it for nearly nine months of the whole 

 year. But in 'most of those insects which as- 

 sume the particular condition of nymph, in 

 which the body remains soft and delicate, as 

 the hornets, ants, and bees, the pupa state is 

 the shortest period of existence, being often 

 scarcely more than a week or ten days. In 

 every species the length of this period is much 

 affected by the influence of external circum- 

 stances. Thus if the larva of the common net- 

 tle-butterfly, Vanessa urtictE, change to a chry- 

 salis in the hottest part of the summer, it will 

 often, as we have found, be developed into the 

 perfect insect in eight or nine days ;* whilst if 

 its change into the chrysalis takes place at 

 the beginning of summer, it is fourteen days 

 before the perfect insect appears ; and if it en- 

 ters the chrysalis state at the end of summer, it 

 remains in that condition through the winter 

 until the following spring. On the other hand, 

 as was proved by Reaumur, if the chrysalis be 

 placed in an ice-house, its development into 

 the perfect insect may be retarded for two or 

 three years. Again, if the chrysalis be taken in 

 the midst of winter into a hot-house, it is deve- 

 loped into the perfect insect in from ten to 

 fourteen days. This period of quiescence is 

 absolutely necessary in all those species which 

 undergo an entire change of form and habits, 

 for the completion of those structural metamor- 

 phoses by which the creature is not only adapted 

 to the performance of new functions, but is 

 equally incapacitated for the continuance of 

 some of those which it has previously enjoyed. 

 During this period it is that new parts are deve- 

 loped, and the insect's mode of life is in conse- 

 quence entirely changed. Whilst these altera- 

 tions are taking place in the organic structures, 

 the functions of the organs themselves are in a 

 great measure suspended, and the condition of 

 the insect becomes that of the hybernating ani- 

 mal. Respiration and circulation are reduced 

 to their minimum,f and the cutaneous expendi- 

 ture of the body is then almost unappreciable 

 even by the most delicate tests. J Thus a pupa 

 of Sphinx ligustri, which in the month of Au- 

 gust, immediately after its transformation, 

 weighed 71.1 grains, in the month of April fol- 

 lowing weighed 67.4 grains, having thus lost 

 only 3.7 grains in the long period of nearly 

 eight months of entire abstinence. The whole 

 of this expenditure, therefore, had passed off 



* Phil. Trans. 1834, part 2, p. 416. 

 t Phil. Trans. 1836, part 2, pp. 555-6. 

 $ Idem. 1837, part 2, p. 323. 



