Antenncp of Insects. 233 
and crevices, from which they almost immediately withdrew them, 
and proceeded in search of others.” As the ichneumons deposit 
their eggs in the larvae of other insects, Mr. Samouelle suggests 
it as probable that in some instances they found the holes empty, 
and proceeded in search of those in which the object was con- 
cealed ; and at the same time lie inquires — since the antennae of 
the ichneumon are not near so long as the ovipositor or tube, 
and consequently could not always have touched the larva in which 
that instrument afterwards deposited the eggs — whether from the 
above facts we may not conclude them to be organs of smelling ? 
It must be acknowledged that these facts go farther in support 
of the opinion than any previously adduced ; but I would inquire 
whether the same facts would not go equally far in proof that the 
antennae are organs of hearing? To this however we shall return 
hereafter. 
In July, 1829, I examined the anatomy of the antenna of a 
male of one of the larger ichneumons, I. Atropos, Step., the species 
that infests the larva of the privet moth Sphinx Ligustri, L. It 
consists of about fifty-six articulations, all of which, excepting only 
the second, from the base to the tip, are gradually diminished in 
size, and perforated all round by very minute holes, those nearest 
the tip having also a few scattered and very delicate hairs. This 
is the general structure of the setaceous antennae of most insects. 
Upon making a section of the antenna, I observed its interior to 
be very copiously supplied with a limpid fluid, and that in addition 
to a delicate nerve in the centre which extended throughout the 
whole length of the organ, were, one on each side, two silver- 
coloured tubes, from which a number of other minute tubes were 
produced at every joint. That these were hollow tracheae I am 
certain, having divided them longitudinally, and observed their 
beautiful silvery appearance within. Their structure in every re- 
spect resembled that of other tracheae.* The exterior or bony 
part of the antennae was perforated, as above noticed, by very 
minute holes, and these seemed to me to communicate with the 
minute tubes proceeding from the larger vessels, but of this I am 
not quite certain. There were so many of these that I counted 
eleven on each side of several of the joints through which the sec- 
tion was made. 
* I have since found that these tracheae are derived from some ciuciform 
branches which originate in the head immediately behind the brain, from the 
superior transverse trachea; which arise, one on each side, from the first pair of 
spiracles, and anastomose in the upper part of the head above the cranial portion 
of the dorsal vessel. See Phil. Trans. 1836, Par. 11., p. 534. 
S 2 
