ON THE STRUCTURE OF THE ANTENNA. 589 
the larger superficial cells, but many apparently end in the small 
round cells beneath them. 
The large Sacculi have an average diameter of 50 u (Pl. XLI., 
Fig. 2, B). Each sacculus consists of a very thin cuticular 
layer, usually inflected so as to form a group of sacs open- 
ing into a single central cavity, more rarely as a simple 
flask-like sac. This membranous cuticle supports a vast 
number of very fine, straight, broad-based sete, which con- 
verge towards, and sometimes project from, the orifice of the 
sacculus. The orifice of the sacculus is generally irregular in 
form, bounded by several short curves; but it is occasionally 
circular, when the sacculus has no secondary sacculi in its 
walls. The nervous structures beneath the sacculi are iden- 
tical with those under the rest of the integument, but the 
large superficial ganglion cells are more numerous in relation 
with the sacculi. I have occasionally seen flame-shaped cones 
in the sacculi, and suspect their origin is similar to that of the 
cones on the surface of the antennae. Those in the sacculi are 
smaller, proportionately to the finer sete which they contain. 
c. On the Functions of the Antenne in Insects generally. 
Oken regarded the antenne as organs of hearing, and 
Lefebvre [262], in 1838, was apparently the first who attempted 
to controvert this opinion and to attribute an olfactory function 
to them. It is true that Reaumur suggested the possibility 
that they subserve the olfactory sense, but he brought forward 
no evidence in favour of this view; and the majority of authors 
who touched upon the subject before 1847 followed Oken. 
Erichson [263], in the latter year, investigated the minute 
structure of the antenne, and concluded from his anatomical 
investigations that they are olfactory organs. Erichson’s 
knowledge of their minute structure was necessarily very im- 
perfect, and, although his conclusion was apparently correct, 
he had no facts to justify it. 
Leydig [122], in 1855, reinvestigated the subject, and traced 
the antennal nerve to the end organs discovered by Erichson, 
although he gave a figure of the olfactory sete of Calliphora, 
