






18 IV—PHENOMENA EXHIBITED BY THE LEPIDOPTERA. 
CHAPTER IV. 
ON CERTAIN PHENOMENA EXHIBITED BY 
THE LEPIDOPTERA. 
In the present chapter it is proposed to give a brief 
account of some of the more interesting phenomena ex- 
hibited by butterflies and moths during their lives, but 
before doing so it will be desirable to present, in the most 
elementary possible form, a general view of the leading 
principles of organic evolution, as set out by Darwin and 
his numerous followers. Prior to the time of Darwin, most 
naturalists were quite satisfied to collect facts, but they 
seldom attempted to interpret the facts, or to draw any 
general conclusions, or deductions, from the masses of in- 
formation they had so laboriously accumulated. The birth 
of philosophic natural history practically dates from the 
publication of Darwin’s ‘‘ Origin of Species,’’ and since 
the appearance of that epoch-making work, new methods 
have been adopted, and the entire study of natural history 
revolutionised. 
The theory of the origin of species, first propounded by 
Darwin, is dependent upon the following indisputable 
faetors :— 
1. Variation. No two individuals are exactly alike. 
There are always some variations from the parent form, 
sometimes slight, sometimes considerable. This is abun- 
dantly shown amongst the New Zealand Lepidoptera, many 
of the species of which are highly variable. 
2. Inheritance. Many of these variations are inherited 
—a fact demonstrated by our domestic plants and animals, 
where man has selected and bred from varieties suitable for 
his purposes, and has thus produced races in which the 
variation is permanent. Many of the races of domestic 
animals differ as much from one another as do some dis- 
tinct species of wild animals. 
3. Struggle for Existence. All animals and plants pro- 
duce far more offspring than ean possibly survive, thus 
giving rise to the struggle for existence. For example: 
The average number of eggs laid by a Lepidopterous insect 
is certainly over 100, and in many species this number is 
greatly exceeded. Assuming each female to lay 100 eggs, 
the progeny from a single pair would amount, after six 
generations, to over six million individuals. 
4. Natural Selection, or the Survival of the Fittest. In 
the struggle for existence which necessarily results from 
such a great increase of individuals, those variations which 
favoured the possessors would be preserved, whilst those 
which did not, would be gradually exterminated. This 
principle of the preservation of the favourable varieties in 
the struggle for life is called Natural Selection, or the Sur- 
vival of the Fittest. 
5. Divergence of Character. As there are so many 
different places and conditions in the economy of nature 
which can be occupied by organic beings differently con- 
stituted, individuals which diverged most from the original 
type would be brought into less severe competition, than 
those which diverged only in a slight degree. For instance, 
if we represent the original form as A, occupying one place 
in the economy of nature; a second form as B, occupying a 
somewhat similar place; a third form as C, occupying a 
very different place to A although somewhat similar place 
to B, it is obvious that B would enter into severe competi- 
tion with both A and C, whilst A and C might not trend to 
any great extent on one another’s place in the natural 
economy ; hence B would be exterminated before either A 
or C. In other words, natural selection continually tends 
to increase the slight differences, which we eall varieties, 
into the greater differences, which we call species. 
In addition, to the operation of natural selection, it 
was formerly considered that the inherited effects of use 
and disuse had played an important part in organic evolu- 
tion, but later investigations have shown that attributes 
aequired by the individual during its own life-time are 
very seldom transmitted to the offspring, and the inheri- 
tanee of acquired characters is not therefore now generally 
regarded as an active principle in organie¢ evolution. 
It has been contended that species have arisen through 
sudden and great variations from the parent stock, which 
have been termed mutations. It is possible, that in isolated 
cases, Species may have sprung into existence through 
sudden favourable variations, but the balance of evidence 
in this, as in most other cases of natural change, is in favour 
of a series of gradual adaptive transformations, by means 
of minute variations, probably extending over a very pro- 
longed period. In connection with the mutation theory, 
mention should be made of Mendel’s Law of Heredity, 
which shows that certain characters are inherited by, a 
definite proportion of the offspring. For instance, in the 
historic example of peas, experimented on by’ Mendel, it 
was found that by crossing tall and short peas, there re- 
sulted in the second generation 25 per cent. of pure tall 
peas, 25 per cent. of pure short peas and 50 per cent. of 
apparent tall peas, and the last named, when subsequently 
seeded, resulted in tall and short peas in similar definite 
