GENERAL NOTES. 
118 
The nuchal horn or retractile process near the head, mentioned at page 106, which 
seems to exist in all Papilio larvae, are pliable, hollow, semi-transparent organs, united at the base 
but forked into two branches, extruded from a slit on the top of the second segment when the 
larva is irritated or alarmed, quivered in the air a few moments and again drawn within the 
segment, the slit closing up completely. If touched from behind, the horn is thrown backwards or 
the larva turns its head and attempts to smear the fingers with its moist surface. This curious 
organ emits a very strong and nauseous smell, which clings tenaciously to anything which is 
touched by the appendage; evidently a means of defence against some of the enemies of the larva. 
This nuchal horn is shown exserted in the figure of the larva of P. antiphates , PI. 4a. The 
pupae of all the Papilionince here, except that of P. clytia , are supported by a girdle of white or 
yellowish silk, but that of P. clytia is black, which certainly harmonizes well with the colours of 
the pupa and its usual environment, for it always appears to pupate against a brown stem or twig, 
whereas the other species often secure themselves to green leaves or branches. Yet the larva of 
P. clytia is brilliantly coloured and a conspicuous object as it rests in full view on the upperside ot 
a leaf; but bright colouring in larvae is generally supposed to be synonymous with nauseous taste 
or odour, and if the warning colour is not sufficient to ward off enemies, the larva will use his 
nuchal appendage. But the pupa is absolutely defenceless, and its best chance of safety lies in 
assimilating so closely to its surroundings that it is sometimes passed over even by the sharp eyes 
of birds and other pupae destroyers. 
As has been noted already, many of the Papilio larvae in their young stages differ 
entirely in colour and marking from the fullgrown caterpillars, and most of them have a series of 
well-marked dorsal processes when very young, nearly all of which gradually disappear as the larva 
grows. The very young larvae do not seem to have the power of putting forth the nuchal horn. 
