98 
THE EXTOMOLOGTST’S RECORD. 
Scotland or elsewhere; thus if m = moisture and p = the 
melanism-producing product, then : — 
2m + ip might have the same effect as im + 2p. 
That is supposing there to be an excess of moisture (2m) 
which held a certain amount of melanism-producing product 
(p), as might be the case in the very moist humid districts, 
then it might have the same effect as twice the melanism- 
producing product (2p) in half the quantity of moisture (im). 
If this were so, we should in effect get the same results in 
the wet districts of Britain as in those less humid districts 
containing more of the melanism-producing product.” Mr. 
Cockerell then goes on : — “ If we assume that im absorbs 
2 p, the products being thus — 
2m + ip = 
im-f2p = mp2 
m P2 (the town effluvium) is here stronger in p than is the 
m2 p, but it is more diluted with air (on the supposition that 
the air has less moisture, and therefore can carry less p) ; so 
that if 2 (m2 p) is diluted in i cubic foot of air, then there is 
m4 P2 to I foot of air; and also if 2 (m p* ) is diluted in 2 
cubic feet of air, then there is m p2 to i foot of air. That is, 
each foot of air contains the same quantity of p. 
This is perhaps badly put, but you will (I think) see what 
I mean.” I think the idea is very well put, and anyone who 
understands the simplest forms of chemical equations, will see 
what Mr. Cockerell means. It must be remembered, however, 
that this is purely theoretical, although it is quite warranted 
by the facts at our disposal. 
{To be continued.) 
The fungus Torrubia robertsii on the larva of Hepialus 
VIRESCENS. — At the beginning of the year 1890, a friend who had just 
returned from New Zealand shewed me two of these larvae which he 
had bought from the natives. At that time I knew little more of their 
life-history than is contained in the E^itomologist (see below) and all the 
information my friend could obtain from the natives did not add much 
to it. According to their version, the peculiar appendage is not fungoid, 
but the result of the larva having eaten a seed of the “Rata” vine (on 
the leaves of which they said it fed), which, having germinated, kills the 
larva, and, continuing to grow absorbs its tissues and produces the 
extraordinary appendage. Such, though very erroneous, is their version. 
Among scientific works, I have only been able to discover in one single 
instance anything of a satisfactory description, sufficient to satisfy the 
