33 
liaving so rapidly forced the insects through the pupa stage, tliat 
tliey had, so to speak, no time to attain their natural size. 
Ihese and kindred subjects derive a special interest from their 
bearing on the great question of the origin of species. Another 
obscure subject requiring much investigation is the periodical 
aiipearance of certain insects. Last year afforded numerous instances 
of this fact. To a certain extent every insect is more or less peri- 
odical in its appearance, and I have frequently remarked, in particu- 
lar seasons, the almost comjiletc absence of what are generally 
common species. 1 believe it will bo found, on examination, that 
a special and different reason for its periodicity exists in the case of 
each individual species, and it is only by carefully studying its life 
history that we can hope to ascertain this cause. Thus, for instance, 
an unusually late frost in INfay may destroy entire broods of young 
caterpillars, especially if they be in a delicate state from having 
recently moulted, or in the case of diurnal Lepidoptera a few wet 
days occurring shortly after they have emerged from the chrysalis, 
may effectually prevent the union of the sexes and consequently the 
impregnation of tlie eggs. 
I must leave this wide field of physiological entomology, and 
glance briefly at a few of the points conqinsed in the last division of 
my subject, zoological entomolog}", which will probably after all 
demand the greatest amount of attention from the entomological mem- 
bers of this Society. One of their first duties, I ima^ne, will be 
to complete, as far as possible, the collection in -the museum, and I 
would suggest that a register, similar to the one recently published by 
]\Ir. Carrington, of York, showing the locality, date of capture, 
captor’s name, &c. bo kept with it. The occurrence of species new to 
the county will of course be recorded and the specimens exhibited. 
The formation of thoroughly authentic local lists, from which I 
hope in time a complete insect feuna of the county may be compiled, 
is highly desirable. The mapping out of the distribution of differ- 
ent species is a subject which shoiddbe especially studied, as it may 
assist us in solving some of the difficult questions connected with the 
distribution ofspecies generally. Many insects are almost as much con- 
fined tocertain localities as plants. Thusc.p. I discovered that very local 
species, Arge galathea, in 18G4, confined to a single marsh in the 
parish of Kirby Cane ; the next year it was just as local but it had 
changed its quarters, having migrated to a contiguous marsh. The 
D 
