10 
THE SUBSTITUTE. 
the ordinary spots are warty, 
always raised, often shininj^, and 
as it were metallic ; each only 
bears a single hair, which is, how- 
ever, visible enough, though short. 
They feed exclusively on the 
lichens which grow on trees or on 
rocks, and like all other lichen- 
ivorous larvie they only lake their 
meals when the lichen is moist 
with dew. As soon as the sun 
has attained any height they 
hasten to regain their places of 
shelter. Those which feed on the 
lichens of trees retire among the 
bark or under the shelter of the 
branches ; but those which are 
situated on stone walls would not 
thus find a sufficient shelter from 
the heat, consequently they spin 
in the cavities or little crinks of 
the wall, small cocoons, which 
they consolidate with pieces of 
lichen and mortar, and through 
which they make a hole to servo 
as a passage of egress. When 
ready for their transformation they 
construct a new cocoon, which 
they cover so cleverly with frag- 
ments of wall that I have seen on 
well-hewn stones, which appeared 
quite smooth, as many as ten to a 
dozen of these cocoons, which it 
was impossible to distinguish at 
the first glance, and to discover 
the whole of which required seve- 
ral hours. 
The Bryoj)hil(E, in the perfect 
state, are small inseets with slen- 
der bodies : their wings are varied 
with brown, whitish and green, 
and imitate, in some degree, the 
lichens on which the larv® have 
fed, on which the insects repose 
quietly during the day, and arc 
almost as hard to be distinguished 
as their cocoons. The object of 
these singular resemblances is 
easily divined, and nature has 
multiplied them in a thousand 
analogous circumstances, evi- 
dently in order to give defenceless 
insects the chance of escaping 
from enemies of all sorts. (Vol. I., 
p. 22.) 
Acronycta. 
Of all the genera of the Noctu® 
this is certainly that in which 
there is the greatest diversity 
among the larvte; j'et the differ- 
ences consist principally of the 
greater or less development of the 
trapezoidal warty spots. Thus, 
whilst in Auricoma, Menyanthidis 
and Rumicis, these are elevated 
into a hemispherical fonn, and 
furnished wiih tufts of hair, as in 
the Chelonidfe, they are much 
reduced in size, and' flattened in 
other species, till, as in Liyustri, 
they only form small dots, hardly 
raised at all. The nature of the 
hairs also, with which they are 
clothed, varies considerably. Long 
and silky, though scattered, in 
Psi, Tridens, Ikc., they become 
thick and disposed in long diverg- 
ing tufts in Aceris ; they cover 
the entire surface of the caterpil- 
lar in Leporina ; they are reduced 
to short brushes in Itumids; in 
Meyacephala there are only a few 
hairs ; in Ligustri only one pro- 
ceeds from each spot ; and in Alni 
these hairs are swollen at the tip 
so as to appear clubbed. Yet the 
length of the hairs and the size 
of the trapezoidal warts are not 
the only variations we observe in 
this singular genus ; even the 
form of the larva; undergoes con- 
siderable modifications. Thus, 
whilst a large number are cvlin- 
drioal, only a little tlatteneil be- 
neath, without any eminence, 
some, such as Psi, Tridens and 
