220 Dr. Wallace on 
the prolonged drought and heat. The disease was first observed on 
the 19th of August, which was a warm sunny day, but the preceding 
days had been rainy and stormy, with one or two cold nights and 
north-west winds. I quote from my diary : ‘ about six larva were 
either found on the ground, or were banging from the leaf-stalk, 
head downwards, clinging by their hind claspers ; they were of a 
pale lilac tint, soft, slightly livid, some darker-looking, more 
sanious, these had been in process of passing through their last 
moult; some of those still feeding-up looked pale and livid, these 
subsequently fell off and died, previously turning livid, and if 
squeezed emitting a sanious black gore; they seemed, too, when 
alive, colder to the touch than was natural.” The larvee which were 
between their second and third moult, also those which had passed 
through their fourth moult and had fed afterwards, seemed to 
escape this epidemic, but the malady chiefly attacked the larvee 
which were undergoing, or on the eve of undergoing, or had just 
undergone, their last moult ; hence I conclude this to be a critical 
period for the constitution of the worm. I find, too, this note: 
‘In the garden near the house a larva, which had been since the 
23rd instant moulting for the last time and completed this change on 
the 26th instant, not having fed afterwards, was found soft and 
dead on the ground on the 27th.”” Hence I infer that if the period 
of moulting, owing to the weather, be prolonged beyond the normal 
period, a great loss of vitality and a tendency to death ensues. 
After the 28th no more deaths from this disease were observed ; 
at that time the weather again became warm and sunny. I calcu- 
lated that at least 200 were lost from this disease, which lasted 
about ten days, during which time I picked up about twenty 
a-day, but it is quite possible that some escaped my observation. 
I ought to mention that some parts of my plantation were 
severely visited by this disease, others scarcely at all affected ; 
that the former portions were in close vicinity with potatoes which 
had been planted in rows between each row of Ailanthus trees 
and in some interspaces, and just at that particular time the 
disease attacked the potatoe haulm, and I had the haulm pulled 
up and gathered in heaps. At a distance from the potatoes there 
were scarcely any instances observed of diseased larvee; but, on 
the contrary, the larve on those trees which were nearest to the 
heaps of decaying potatoe haulm were nearly all destroyed by 
this singular epidemic. I am, therefore, inclined ina great measure 
to attribute it to a vitiated atmosphere permeating their trachee 
and poisoning their blood juices at a critical time when they were 
weakened by the prolongation of their last moult. This one thing 
