THE INTERNAL STRUCTURE OF THE LEPIBOPTEROUS PUPA. 83 



With regard to the integument of the imago, Packard writes that 

 the portion of the wing-sac which persists when the pupal-wing 

 passes to the exterior {i.e., the hasal portion, the " peripheral pad" of 

 Bugnion, or the " annular zone " of Kiinckel), serves at first to attach 

 the appendage, whilst forming, to the hypodermis of the larva, then 

 afterwards, to more or less completely regenerate the adjoining portion 

 of the integument. In this way, the hypodermis of the thorax is 

 partially, that in the head is almost entirely, replaced by the imaginal 

 epithelium which proliferates at the base of the appendages, while 

 that of the abdominal segments persists, at least in a modified way, 

 and only undergoes, at the end of the pupal period, transformations as 

 regards the appearance of the scales and pigment. 



Eeference to Newport's figures (Imecta, 1839) of the internal 

 organs of the larva, pupa and imago of Sphinx ligustri will convey a 

 better idea of the changes that occur in the digestive organs than any 

 amount of description. Eeference to these will also show that the 

 alimentary canal of the pupa is almost as much differentiated as is 

 that of the imago, though the reservoir or " sucking stomach " of the 

 imago is not indicated in the pupa. These changes are quite in ac- 

 cordance with the needs of the animal and accommodate themselves to 

 the great change that occurs in an insect which has passed from a larva 

 with an enormously voracious appetite to an imago that exists on a 

 small quantity of water and nectar or that practically abstains from all 

 food. Corresponding with the reduction in the size of the alimentary 

 canal, the salivary glands and other organs actively employed in the 

 processes of larval digestion undergo a thorough reduction. Newport's 

 figures are reproduced by Packard {Textbook of Entomology, p. 646, 

 figs. 598-600). 



The smaller tracheae, and even some of the larger branches, 

 undergo destruction with those of the larval structures to which they 

 belong, when they disappear as already described, whilst similar ones 

 arc devekpsd in the imagmal structures which take definite form at this 

 pencd. One portion of this development has already been described 

 as pi.rL cf the growth of the imaginal discs of the young larva into 

 the pupai wings. The changes in the general plan of the tracheal 

 trunks and their main branches are not so sweeping as occur in the 

 higher Diptera. The great change that occurs is the development of 

 larger trunks and more numerous branches in the thoracic and cephalic 

 regions and the destruction without replacement of abdominal trachea?. 

 In the larva, the prothoracic spiracle is an important one. It is, if 

 anything, more so in the pupa. The mesothoracic spiracle, which 

 does not exist in the larva, is present in the pupa, though it can hardly 

 be said to be functional, being, like the first abdominal one, covered by 

 the wings. This spiracle possesses a representative in the larva in a 

 fine filament passing from the skin at the junction of the meso- and 

 metathorax to the tracheal trunk. At the moults, this filament 

 serves to draw out, with the skin, the tracheal lining of the adjacent 

 trunk and branches. The track of this filament is no doubt supplied 

 with embryonal cells, which replace it at each moult, and, with others 

 beneath the hypodermis, form, in fact, an imaginal disc for the 

 development of the (pupal and) imaginal spiracle and tracheal trunk. 

 More important, if anything, in the larva, than the first spiracle, is tho 

 last, that of the 8th abdominal segment. At the change to pupa, 



