876 



INSECTA. 



change weighed only about nineteen or twenty 

 grains, at the expiration of eight days when it 

 was full-grown weighed nearly one hundred 

 and twenty grains. Most larvae immediately 

 after changing their skins remove to fresh 

 plants, but some, as the larvae of a beautiful 

 moth, Episema caruleocephala, devour their old 

 skins almost immediately they are cast, and 

 sometimes one another when deprived of food. 

 But it is not merely the external covering 

 which is thrown off during these changes ; the 

 whole internal lining of the alimentary canal 

 also comes away with the skin, as was formerly 

 noticed by Swammerdam,* and repeatedly ob- 

 served by ourselves and others. The lining of 

 the mouth and pharynx with that of the man- 

 dibles, is detached with the covering of the 

 head, and that of the large intestines with the 

 skin of tlie posterior part of the body, and 

 besides these also, the lining of the tracheal 

 tubes. The lining of the stomach itself, or that 

 portion of the alimentary canal which extends 

 from the termination of the esophagus to the 

 insertion of the so called biliary vessels, is also 

 detached, and becomes completely disintegrated, 

 and appears to constitute part of the meconium 

 voided by the insect on assuming its Imago 

 state. Herold, however, has denied that this 

 change ever occurs in the alimentary canal, and 

 says that in the trachea it takes place only in the 

 larger stems. But Swammerdam states that he 

 saw it in the larva of the rhinoceros beetle, 

 Oryctes nasicornis, which shed both the lining 

 of the colon, and of the delicate as well as larger 

 branches of the tracheae,f and BonnetJ had wit- 

 nessed a similar occurrence. Burmeister has 

 also seen it, both with respect to the colon and 

 tracheae, in some of the Libellulse, and we now 

 add our own testimony to the fact of its occurring, 

 not simply at the extremities of the canal, but 

 throughout its whole extent, as we have dis- 

 tinctly seen during the changes of the nettle-but- 

 terfly, Vnnessa urtica.\\ It is more distinctly 

 observed when the larva is changing into the 

 pupa state than at any other period, although 

 we believe that it really does take place at 

 every change of skin. Hence these changes 

 are of the greatest importance to the larvae, 

 which often perish during their occurrence. 

 They are undergone by all larvae which possess 

 the true organs of locomotion, but it has been 

 questioned whether they are common also to 

 the apodal larvae, more particularly those which 

 constantly remain in the same locality until 

 they have changed into pupae or nymphs. 

 Reaumur and Hubert state that the larva of 

 the common hive-bee does not change its skin, 

 but only grows larger ; Swammerdam,** on the 

 contrary, asserts that it does, and also that he 



* BibliaNat. 



t Biblia Nat. p. 129, 134, 239, &c. 



Contemplation de la Nature, torn. ii. p. 48. 



$ Manual of Entomology, (Trans.) 1836, p. 428. 



|| Since these remarks were written, a paper by 

 Mr. Ash ton upon this subject has been read at a 

 late meeting of the Entomological Society, Nov. 5, 

 1838, in which the statements of Swammerdam 

 respecting these changes have been fully confirmed. 



f Kirby and Spence, Introduc, vol. hi. 



** Biblia Nat. p. 163, a. 



has observed the same thing in the alimentary 

 canal of the hornet.* Burmeisterf believes that 

 it does not take place, and states positively 

 that the larvae of Diptera do not moult. We 

 have watched for these changes in the larvae of 

 the wild bee, Anthophora retusa, but have been 

 unable to observe them, although we believe 

 they do really occur. But the universally ac- 

 knowledged accuracy of most of Swammer- 

 dam's observations, supported as they are in this 

 instance by analogy, fully warrants us in con- 

 sidering this subject as still open for enquiry. 



When a full-grown larva is preparing to 

 change into the pupa state it becomes exceed- 

 ingly restless, ceases to eat, and diminishes 

 much in weight. Many species spin for them- 

 selves a covering of silk, termed a coccoon, 

 or case, in which they await their transforma- 

 tion. Others prepare little cavities in the earth 

 and line them with silk for the same purpose, 

 (Jig. 363), and others suspend themselves by 



Fig. 363. 



Section of the coccoon or winter nidus of Atha.Ua 

 centifolifB, natural size and magnified. Newport, 

 Prize Essay. 



their anal prolegs to the under surface of a leaf. 

 In each of these instances this important change 

 takes place in the same manner. Before the 

 larva thus prepares itself for metamorphosis its 

 alimentary canal is completely evacuated of its 

 contents, its body, as at the previous changes of 

 skin, becomes dry and shrivelled, and much 

 contracted in length, and certain enlargements 

 at the sides of the anterior segments indicate 

 the now rapidly developing parts of the future 

 pupa. These changes take place in all insects 

 in a similar manner, but have been most fre- 

 quently watched in Lepidoptera, upon which 

 also our own observations have been made. 

 We have also observed the same changes in 

 Hymenoptera. The larva of the sphinx, when 

 it is ready to undergo its changes, penetrates 

 the earth to the depth of a few inches, and 

 there forms for itself a little chamber, in which 

 it awaits its transformation. But the butterfly 

 either fastens itself by a little rope of silk, 

 carried across its thorax, to the under surface 

 of some object, as a ceiling, &c., or suspends 

 itself vertically by its prolegs, with its head 

 directed downwards, as is the case with the 

 common nettle butterfly, Vanessa urtica. We 

 have watched these changes with much care in 



* Ibid. p. 133, a. 

 t Transl. p. 432. 



