OF THE ANTENNÆ OF INSECTS. 391 
They exist on the last nine segments more towards the distal end of each. The different 
forms are shown at N. fig. 3 a a, fig. 4. : the diameter of the closing-in membrane is about 
5700 inch; the length of the sac is from qayo to tyy inch. 
But, besides, there is another form of what seems to be the same structure, and which 
has a rather less-marked parallel in the antenna of Pronœus inetabilis (to be described 
next). There will be observed at N. fig. 1 bbb, a number of small closing-in membranes, 
of a diameter of 3550 inch; behind each is a very small sac, leading to a long delicate 
tube, which, bending towards the base, dilates into an elongated sac having its end in- 
verted, as may be also seen in the larger sacs (see N. figs. 2&3). What their specific 
use may be, it is at present impossible to say ; but, supposing these organs to be auditory, 
we may easily conjecture that they would be able to appreciate notes in a higher key. 
The nerve in this antenna is well seen, throwing off branches to the organs in its course 
upwards. 
The antenna of Pronœus inetabilis consists of thirteen segments, and possesses three, 
if not four forms of these organs, disposed in groups on one side of each segment :— 
First. In the middle of the segment are a number of small closing-in membranes, 
of the diameter of zzo inch; they are raised above the level of the surface, and have a 
small elongated cavity behind them, which is shown at O. fig. 1 dd, fig. 3 d. 
Secondly. On the side are level, circular or slightly oval closing-in membranes, with 
an oval opening just beneath, leading into sacs; in the centre of each inner surface is 
a papilla pointing inwards. These are shown at O. fig. 100, fig.35. The diameter is 
3300 inch. 
Thirdly. There is a scanty group of organs towards the middle of the segment, whose 
closing-in membrane is also level and quite circular ; and beneath it is a shallow cavity, 
having a small opening in the centre leading into a tube, which soon dilates, and is con- 
nected with a curved tube, which expands in the form of a trumpet. The exact method by 
which these trumpet-shaped expansions end internally is difficult to decide, owing to the 
delicacy of the parts and the thickness of the antenna-wall. It is impossible to make out 
the exact nature of the junction at the curve. This form I have shown at o. fig.1ec, 
fig.3cc. There is a strong resemblance between these and the long expanding tubules 
in Myrmica; and they probably have the same function. 
Bourthly. On shay sede portion of the half-antennal surface occupied by ur 
structures, are a number of low projections, at first sight like dwarf hairs ; but uec 
inspection they will be found to be conical projections of a delicate pe > 
from the centre of a depression of the cuticle, and having a sac behin ss 
nerve can be plainly seen passing, as in the other forms; m i rn ri real 
matter may be observed at the junction of the nerve with the sacs. å Fu m 
analogy between these organs and true hairs. Their diameter is 5560 inch, an pw 
shown at O. fig. 1 a a, fig. 2. å | 3 
That these different å are capable of imparting to im PER se Å EE 
iati : : - ied, if we admit that they are auditory 
ciating notes of different pitch, will scarcely be denied, «må mlt to explain the reason 
Organs; while, if considered as olfactory, it would be ——— | 
of such a variety of forms. 
