THE ENTOMOLOGIST’S 
WEEKLY INTELLIGENCER. 
No. 132.] 
THEORY AND PRACTICE. 
The records of observations lead to de- 
ductions; if such deductions are mani- 
fest and obvious we do not call them 
theories. It is not a theory that the 
weathercock points to the wind ; it is 
not a theory that the night is darker 
than the day ; it is not a theory that 
butterflies fly by day; it is not a 
theory that the larvae of the Common 
White butterflies feed on cabbage. 
Why should it be a theory that the 
larva of Sphinx Convolvuli feeds on the 
bindweed ? 
When an explanation of anything is 
far from obvious and very far-fetched, 
it is not very inaptly termed a theory, 
though that is not the proper meaning 
of the term. For instance, a popular 
writer lately traced the derivation of 
the name Machaon, for the Swallow-tail 
butterfly, to the Latin word machcera, 
a dagger, in allusion to the prolonga- 
tions of the hind wings resembling 
daggers; such an explanation, utterly 
at variance with the truth, might be 
considered as a theory. 
And, still more lately, another writer 
has deduced the name Convolvuli, for 
the Sphinx so called, from its habit 
of frequenting tubular flowers, which, 
[Price Id. 
according to him, led to its being 
named after its favourite plant, and 
thus propagated a delusion that the 
larva fed thereon. 
We never read a more outrageous 
insult to our common sense ; the as- 
sumption that the perfect insect fre- 
quented the flowers of the Convolvulus 
was perfectly gratuitous. Who ever 
heard or read of its doing so? The 
second assumption, that it hence re- 
ceived the name Convolvuli, was like- 
wise contrary to the fact, and must 
surely have been known to the writer 
to have been so: having demolished 
the two premises, what becomes of the 
conclusion ? 
Two gentlemen took the trouble to 
point out to the writer alluded to the 
fallacy of his assertion ; he thanks 
them nonchalamment, terms their facts 
theories, and reposes serenely on his 
own . 
We leave a blank, for we find no 
word to express our meaning’: it is 
perfectly possible for a person to call 
the facts cited by an adversary theories, 
but we cannot conceive such an hallu- 
cination as to lead to a disputant 
calling his own theories facts. 
But the whole episode, from which, 
for the sake of our younger readers, 
we have wished to deduce a whole- 
SATURDAY, JANUARY 29, 1859. 
T 
