352 PRACTICAL AND SCIENTIFIC ZOOLOGY. 
manner, either with eyelike spots, or delicate stripes, so 
that the species can be easily detected. As what we have 
already said, on this subject is intelligible even to the 
student, there seems no occasion to dwell further upon 
the distinctions of Syecies. 
(432.) Varieties, in a state of nature, have their 
origin from some unusual, local, or accidental cause, 
either in their birth, their situation, or their food : they 
do not perpetuate the peculiarities they possess ; but, 
the causes being removed, nature returns again, as it 
were, to her original type. Scanty food produces dwarfs, 
so also does unusual heat or cold with insects removed 
from that temperature most congenial to their consti- 
tution. Varieties, generally speaking, are rare, even 
where the species from which they vary are common. 
As they are evanescent, so they need hardly be described, 
except to illustrate something more than the bare fact. 
(433.) We have now laid before the young natu- 
ralist the essence of those general principles which have 
been more fully and more scientifically discussed in a 
former part of this volume. He may possibly be dis- 
posed to question the necessity of grounding himself in 
this sort of information, but he may rest assured that 
it will give to his more immediate pursuits, and to his 
future progress, a degree of interest and of facility which 
no other plan of study can produce. The more tho- 
roughly we understand the groundwork of any depart- 
ment of knowledge, the more rapid will be our subsequent 
advancement in its details. These preliminary chap- 
ters, on the principles of his science, should therefore 
be perused until their substance is impressed upon the 
memory ; he will then be better qualified to understand, 
and to be interested in, the more enlarged views already 
taken of the subject : while the amateur, not desiring to 
be profoundly versed in the philosophy of that which is 
to him a mere recreation or amusement, may at once 
proceed to the following chapter. 
