154 
[December, 
and only a fluid — a secretion — and not rather a portion of the 
substance of the animal itself ? The larva) of G-. raphani are 
furnished with similar latero-dorsal tubercles, of which the four on 
the meso- and metathorax are the largest. On the upper surface of 
these a minute puckered pore may be observed. But, although 1 have 
been breeding these larvae for years, it is only recently and accidentally 
I have discovered that under peculiar circumstances (circumstances, 
however, reproducible at pleasure) the larva emits from these tubercles 
a double row of clear liquid-like (stalked ? and) capitate protrusions, 
which, coming and going simultaneously, instantly brought to mind 
the figure in Iv. & S. on plate xviii. The conditions requisite for 
evoking this phenomenon in the case of O. raphani, are exposure to 
strong sunshine in a close moist atmosphere. The larva) may then be 
observed as with a row of glass bead-headed pins stuck in on either 
side. But, at the least disturbance, these instantly disappear, so that 
I could not touch them to see whether they were fluid or not. They 
do not seem to be accompanied with any smell. It was only afterwards, 
under different circumstances, I was able to arrive, with tolerable 
certainty, at the conclusion that these bead-like processes from the 
Gastrophysa larva are not a liquid secretion, but an everted portion of 
the insect itself, rather comparable to the horns of certain caterpillars. 
In what I call a double batch of between 80 and 90 eggs laid 
(August 26th) by a $ which, having been originally kept as a virgin, 
and which in that state laid some parthenogenetic eggs, was afterwards 
allowed to become impregnated, but became so only to an imperfect 
extent, — in this batch, along with some perfectly healthy larvae, I found 
many that perished in the hatching, and among these several in which 
these protrusions from the four thoracic tubercles were very striking. 
They were quite analogous to those observed in the older larvae, and 
were emitted from the same parts, viz., the pores of the latero-dorsal 
tubercles of the thorax, the only part out of the shell ; and as they 
were no longer spherical, but elongate finger-shaped, and as they per- 
sisted for many hours — in fact, were never withdrawn, during which 
time they exhibited lateral twitching movements, I could not doubt 
their non-fluid nature. And this has suggested to me, that in the 
case of Lina populi also, the main portion of the extrusion underlying 
the milky, opaque, odorous fluid, may be an analogous solid portion of 
the animal itself. 
Milford, Co. Donegal : 
October , 1880. 
