148 
its second molt, being now 2.12 mm. 
long. It then eats out the parenchyma, 
making a small irregular roundish blotch 
from which it cuts out the little oval 
‘ase in which it pupates. Its length 
after it has finished feeding is 4.24 mm. 
The larva hibernates ; in all of its stages, 
except as hereinafter stated, it is pale 
yellow with a fuscous spot on the under 
surface of each segment except the head 
and anal segment, and two hairs (one 
of them very small) project from each 
side of each of the 
The body is cylindrical and depressed ; 
feet are represented (7) by sucker-like 
dises, and the trophi from its exit from 
the egg are of the ordinary form, that is 
the spinneret, maxillae and palpi are dis- 
tinct, as well as the other organs. Each 
molt in the mine occupies twelve hours. 
It is only recently that I have been able 
to follow its life history, having formerly 
supposed that it molted only once. The 
width of the head of each cast is, 0.101, 
0.202, 0.303 mm. I give these figures 
as showing the regularity of the relative 
sizes of the same insect at its different 
molts. But it will be observed that there 
ure two ratios. In Aspidisca and Nepti- 
cula the larva in each stage increases its 
length by adding the length of the prece- 
ding stage, as 1.06, 2.12, 4.24 mm. and 
0.8, 1.6, 3.2 mm. ; whilst in Lithocolletis, 
Leucanthiza and others the length of the 
larva at the end of its first stage is added in 
each of its succeeding feeding stages (0,81, 
1.62, 2.43, 3.24, 4.05 mm.). In Aspidis- 
ca and others what corresponds to the third 
molt of Lithocolletis and others seems to 
be skipped, and a double length added 
at the fourth. In many larvae there is, 
however, a fifth molt, which seems to be 
same segments. 
PSPECHE. 
the equivalent of the sixth one in Litho- 
colletis, the fifth also being skipped. 
The larva undergoes another (its 
third) molt in its case, after the case has 
been attached for pupation, but previous 
to the molt by which the pupa is formed. 
If the case is opened, some days after it 
has been finally attached, a white silken 
cocoon will be found inside, fitting closely 
to the body of the pupa, and the cast 
skin will be found between the cocoon 
and the case. There are therefore four 
larval stages. In the last stage the 
appearance of the larva differs greatly 
from that of the previous stages. It is 
now yellow, without maculae, and the 
sucker-like spots on the thoracic segments 
have disappeared. I have long known 
the larva in this condition, but only 
recently discovered that it attained it 
by a third molt, though the difference 
in its appearance suggested as much. 
Prof. J. H. Comstock, in his ‘*Report of 
the Entomologist of the U.S. Department 
of Agriculture, for the year 1879,” pl. 2, 
fig. 2, b and ¢, gives figures of these last 
two (or third and fourth) larval stages. 
The mode of progress in the larvae of 
Aspidisca is one of the most surprising 
in the insect world. As above stated 
there are no true feet or prolegs; every 
vestige of them has vanished except on 
the second and third thoracic segments, 
where they are represented (?) by the 
little sucker-like dises before mentioned. 
But these discs are not suckers. They 
are distinct depressions both on the ven- 
tral and dorsul surfaces. They do not 
exude any glutinous or other secretion 
by which the larva gains foothold. The 
larvae are thus apparently without any 
means of porgress. Yet encumbered by 
