Urticating Properties of Porthesia similis. 425 
Kuropean forms. Nor is there a great difference in the 
structure of the spicules, those of C. pityocampa being 
merely devoid of the triradiate barb at the thicker end. 
The spicules of C. pityocampa have been variously said 
to contain formic acid, cantharidin, and no poison at all. 
Deegener, in the “ Handbuch der Entomologie,” seems to 
favour the theory of a combined chemical and mechanical 
action. I have found that the irritating effect of the 
spicules of this species is in no degree impaired by pro-— 
longed immersion in various solvents such as ether, alcohol, 
and xylol. On the sixth and seventh abdominal segments 
of the larva of P. similis there are two eversible glands 
which have been supposed to secrete a fluid which poisons 
the spicules. Of this there is no satisfactory evidence. 
The glands have probably a repugnatorial function. They 
have been described by Poulton (Trans. Ent. Soc. 1887, 
p- 300). The drop of moisture which often appears on 
these structures has no action on either red or blue litmus 
paper, nor indeed have I been able to detect any peculiar 
odour associated with them, though others seem to have 
noticed something of the kind. 
To turn now to the imago. When full fed the larva 
spins a thin but tough cocoon, compounded of silk with 
which its own large hairs are interwoven. The inner lining 
of the cocoon is of much looser silk, and though spicules 
are scattered all through it there is a particularly dense 
mass of these arranged roughly in a belt round the inside 
of the lining, and placed towards the anterior end, a little 
beyond the middle, Fig. 3, S. The spicules adhere together 
in small masses probably owing to their barbed structure. 
By taking pupae out of their cocoons I was easily able to 
show that the moth obtains its spicules from the cocoon, 
since an imago hatched from a naked pupa never has any 
of these bodies in its anal tuft. I then carefully watched 
the emergence of imagines from naked pupae in order to 
see if there could be observed any appropriate movements 
which would result in the collection of the spicules. A 
male on emerging immediately crawled to the side of the 
box and assumed a position suitable for the expansion of 
its wings. The behaviour of a female was, however, quite 
different. Once out of the pupal skin it began a series of 
curious contortions of the abdomen. The latter was 
moved so that the anal tuft described a succession of 
circles, whilst by longitudinal expansion and contraction 
