Dr. T. A. Chapman on Heterogyna penella. 147 
of the rounded posterior part of the pupa; brittle though 
this may be when its functions are completed and it is 
dried up, it is very tough and impervious whilst in use. 
Above, the moist body of the moth covers the eggs and is 
itself sheltered from evaporation by the anterior part 
of the pupa case. The cocoon again must prevent any 
very rapid circulation of air outside, and the eggs them- 
selves form a dense solid mass. 
Protection of the eggs against evaporation, or rather 
against desiccation, is a matter of imperative necessity for 
all insects in a hot and dry climate, and, indeed, under 
most circumstances. Usually, at least with our British 
Lepidoptera, this is secured by a position on or amongst 
herbage. Frequently laid on a leaf, the lower surface 
is thinner than the upper and absorbs moisture from 
the leaf as quickly as it evaporates from above. A very 
dense shell is another expedient, as in Orgyia antigua, 
which has to exist for a long period, otherwise unprotected 
and unassisted. One advantage of the position in which 
the eggs of Micropteryx and Adelids are laid, viz., inside 
the plant tissues, is its moisture. One use, probably of 
the ribbing and flanging on the eggs of many butterflies 
- and Noctuz, is the impediment it offers to a rapid circula- 
tion of air over the egg surface, and those eggs that are 
enwrapped with hair and scales by the parent moth, 
benefit most from it, probably by the protection against 
desiccation so afforded. It is certainly not as a protection 
against cold, as its suggestion of blankets and swansdown 
at first makes us believe. It is not to hide them, since in 
most cases it makes them more conspicuous. It may be 
to make them more difficult of access to smaller foes, and 
unpalatable to larger ones. But no one who has tried 
to clean such an egg of its covering, and found how closely 
it is covered with scales and hair, and how difficult it 
often is to get a view of even a portion of egg shell 
after prolonged efforts to clean off the scales, can doubt 
that they must be very efficacious in preventing evapora- 
tion, both by their own thickness and that of the gum 
which attaches them so closely, and by their loose outer 
layers. Probably not a few of the less understood pe- 
culiarities of eggs have some reference to this protection. 
Without denying that the protection provided in /. 
penella may be against enemies and parasites, as well 
as against drying up, it must be regarded as a remarkable 
