256 B. GRASSI AND A. SANDIAS. 
retain a certain amount of moisture; for if the insects are 
shut up with nothing but particles of cork they all die in a 
few days. 
To sum up, two conditions are essential for the life and 
well-being of Calotermes—a suitable temperature and a 
suitable amount of moisture. But whereas increase of tem- 
perature is favorable, at least up to a certain point, the degree 
of humidity can vary only within very restricted limits. 
Owing to the severity of the winter, Calotermes is absent 
from Lombardy, Piedmont, and Venetia, but it is found in the 
province of Genoa; its northward distribution is not accurately 
known. At Catania it is much more sluggish in winter than 
in summer, the ova do not develop, and the larve and nymphs 
do not moult. The influence of moisture has been repeatedly 
referred to; it is correlated with the nature of the cuticular 
structure (chitinous layer), which except in a few regions, such 
as the mandibles, is very thin, even in the adults and royal 
pairs, in both of which it is brown in colour. The younger 
the individual, or the more recent its ecdysis, the thinner is 
the chitin. In general the rule holds good for Calotermes 
that white and semi-transparent examples have a thinner 
cuticle than those which are more opaque and inclined to 
yellow (very old soldiers or substitute-queens). Young or 
freshly moulted specimens, usually distinguishable by their 
greater transparency and whitish or rarely faintly yellow colour, 
always require more moisture than those which are older or 
have not cast their skin for some time, and possess a more or 
less evident yellow tint. The imagos, before or after the loss 
of their wings, can endure a greater degree of dryness; but 
even these generally die in a short time if removed from the 
wood and exposed to._the open air. 
These conditions of temperature and moisture, naturally 
with some variation in degree, especially of the latter factor, 
must hold good for all other species of Termitide, and are 
probably correlated with their limitation to warm countries, 
their much wider European distribution in epochs when the 
mean temperature was presumably higher, and with their 
