150 Function of the Hairs in certain Lepidopterous Larva. 
1932, but it was again performed with A. caja larvae during 
the present year, 1933. This time, after the larvae had been 
shorn, they were replaced on the food plant for five days so 
that any possible bleeding from the cut hairs should have 
ceased. Operations were then repeated as before. 
In every case the larvae were in their last instar as this 
facilitated shearing. It is understood, of course, that the loss 
of weight recorded includes loss of carbon dioxide as well as 
loss of water, but this does not invalidate the general results 
of the experiments, as the carbon dioxide loss is relatively 
much the less. 
SPECIES 
Year 
Charac- 
ter of 
Larvae 
No. 
Length of 
Experiment 
Original Weight 
Final Weight 
Loss of Weight 
Percent- 
age of 
Loss 
A . caja 
1932 
Shorn 
8 
14 hrs. 
7-2020 gms. 
6-9990 gms. 
0 '5 0 3° gms. 
7-0 
(a) 
Hairy 
8 
14 hrs. 
5-8171 gms. 
5-5819 gms. 
0-2352 gms. 
4-0 
A . caja 
1932 
Shorn 
7 
10^ hrs. 
7‘ 2 7 I 3 gms. 
6-7894 gms. 
0-4819 gms. 
6-6 
(b) 
Hairy 
7 
io4 hrs. 
7-4765 gms. 
7-2012 gms. 
0-2753 gms. 
3-7 
A . caja 
1933 
Shorn 
7 
16^ hrs. 
7-6288 gms. 
7-2875 gms. 
0-3413 gms. 
4'5 
(c) 
Hairy 
7 
i6| hrs. 
12-6720 gms. 
12-4061 gms. 
0-2659 gms. 
2-1 
D. lubrici- 
1932 
Shorn 
7 
24 hrs. 
2-4371 gms. 
2-0899 gms. 
0.347 2 gms. 
I 4 "2 
feda 
Hairy 
7 
24 hrs. 
2-2646 gms. 
1-9373 gms. 
0.3273 gms. 
I 4 - 4 
Conclusions . — The results would seem to warrant the 
following conclusions : — 
(1) As the percentage of loss in the 1933 experiments was 
less than that in those of 1932, it would seem that there had 
been at first a small amount of loss of water from the cut hairs. 
(2) In some species, e.g. Arctia caja, but not in all, e.g. 
Diacrisia lubricipeda, the hairs do actually function in reducing 
loss of water from the body. 
(3) From a comparison of the results with the two species, 
it seems that the rate of loss may be partly dependent on the 
size of the body, the larger larvae losing relatively less water 
than the smaller larvae ; if this be so, it will be in harmony 
with the general relation between body weight and surface 
functions. 
Note. — It is difficult, if not impossible, in the present state 
of our knowledge, to state whether the reduction of transpira- 
tion due to the hairs in some cases is merely a result of the 
presence of the hairs or whether it is functional, and so of 
actual physiological value — and therefore of survival value — 
to the species ; as it occurs in some species and not in others, 
the latter would appear to be the correct view, though we 
cannot yet state in what direction the value may lie. 
The Naturalist 
