METAMORPHOSIS IN LEPIDOPTERA. 19 



quiescent period is reached, the larva has usually been for some little 

 time restless, and has ceased to take food, whilst its dry hard excre- 

 ment appears to be almost exclusively formed of fragments of the 

 intestinal epithelium (Packard), and are often stained red by the 

 secretions of the urinary tubes (Gonin). With regard to the faecal 

 deposits at this period, Chapman notes that when the larva of PJtaretra 

 (Arsilonclie) venosa is ready to spin up, it voids some damp frass very 

 unlike the dry material of a feeding larva, shrinks very much in bulk, 

 diminishing in length from 45mm. to 33mm., whilst the colours lose 

 all definition and brightness. P. auricoma has a somewhat similar 

 habit of shrinking in size and voiding moist frass before spinning. 

 Chapman thinks this is really a somewhat universal habit, though 

 varying much in degree, the large silkworms, Antheram yamamai, 

 Samia cecropia, &c, voiding some actual fluid when preparing to spin. 



The same observer notes that it appears to be a common occurrence 

 for many Lepidoptera to inflate the intestinal canal with air when about 

 to moult. The larva of 8. cecropia, just before spinning its cocoon, 

 discharges, with the last contents of the intestinal canal, from 30-50 

 minims of clear fluid, which soon becomes brown, and various other 

 Bombycids do the same. Nevertheless the larva does not diminish in 

 bulk, the intestinal tube remaining inflated with air. This, he says, 

 is "easily tested by scratching the tubercles of the larva, when a 

 hollow sound results, hardly any sound being produced by so treating 

 a feeding larva." He has further determined by dissection that it is 

 air that is in the intestine. 



The larva is much shortened and thickened during the quiescent 

 period preceding pupation, the thoracic segments often appear to be 

 much contracted longitudinally and bulged (due probably in part to 

 the contracting of the thoracic muscles), and if, at different periods 

 during this stage, the larva be hardened in alcohol, and the larval skin 

 taken off, the semipupa, pronymph or propupa (of different authors) 

 will be found in different stages of development. With regard to 

 this change in shape it may be mentioned that the mesothorax of the 

 pupa is much its largest segment, for the development of the great 

 muscles used in flying ; the wings and legs attached thereto also 

 occupy considerable space just before pupation. Consequently the 

 thoracic segments are, at this period, much bulged, the larval skin 

 often distended apparently to its utmost limit, whilst the appearance 

 of contraction is due to the tenseness of the incisions and the com- 

 parative shortness of the ventral skin. We may further note that, 

 in a larval moult, the skin usually remains fixed to a silken pad, whilst 

 the larva creeps out of it. In the pupal moult there is no such 

 assistance, and this swelling of the thoracic segment is also, no doubt, 

 mechanically useful in the rupturing of the larval skin, without too 

 much vermicular effort, although the swelling itself is probably aided 

 by some slight vermicular efforts during the resting period. Chapman 

 also notes that before the larval skin is moulted in Sphinx Ivjustri, the 

 relative size of the segments has much changed, the prothorax being 

 large, the first abdominal very small, whilst he observed that the 

 margin of the mesothorax against the 1st spiracle was already brownish, 

 as well as the flanges on the 5th, 6th and 7th abdominal segments. 



Newport describes the mode of moulting the final larval skin (of 

 Aylaia uiticac) as follows : " The skin bursts along the dorsal part of 



