] 40 Transactions of the Royal Microscopical Society. 
me very clear. The mouth sac appears to lie well above the 
proboscis, so that the retraction of the latter could not, I thiuk, 
exercise much pressure on the sac, while the contraction of the 
lingualis, from the relative position of the parts, as shown in 
Brants’ figure, would, as it seems to me, depress the upper walls 
of the mouth sac, and therefore diminish the cavity. I merely, 
however, suggest these as difficulties which have occurred to me, 
and I have great hesitation in expressing an opinion in opposition 
to that of so good and careful an observer as Dr. Brants. 
The explanation, however, which Dr. Brants has given stands 
necessarily in connection with the function which he attributes to 
the mouth sac. As he very truly observes, in attempting to deter- 
mine the function of the mouth sac, we must have regard to the 
habits of the species in which it occurs. He discovered it, as we 
have seen, in wasps, and considers that it is absent in bees ; hence 
he infers that it is connected either with the construction of the 
paper-like cells of wasps, or with the manner in which they feed 
their larvae. Adopting the former view, he considers the mouth sac 
to be an organ in which the cement is prepared with which the 
particles of wood and other substances are glued together to form 
the paper-like material of which wasps’ nests are composed. 
As, however, Meinert has pointed out, this theory is scarcely 
tenable if we consider that ants also, which do not, as a general 
rule, build in this manner, also possess a mouth sac. 
In fact, as it seems to me, the contents of the mouth sac are 
not intended only to pass outwards through the mouth, but, on the 
contrary, into the oesophagus through the pharynx. Hence it is 
natural that I should regard the mechanism from a different point 
of view. 
In ants, as it seems to me, the general action of the muscles 
which open the pharynx would tend to empty the mouth sac ; those 
which draw down the lower wall of the pharynx, by directly con- 
stricting the mouth sac, while even those attached to the upper 
wall of the pharynx would tend to empty the mouth sac by suck- 
ing out its contents. The muscles of the pharynx, as will be 
seen by the figures, are very complex. 
The anterior wall of the pharynx is drawn downwards by the 
muscles (Plate CLXXXIX., Fig. 1, and Plate CLXXXIX., Fig. 3, 
p m 1 and p m 2) which pass from the anterior wall to the clypeus ; 
it is extended laterally by the muscles (Plate CXC., Fig. 2, p m 3) 
which pass forwards and outwards, to be attached to the head close 
to the base of the antennae, while it is drawn backwards and 
upwards by the muscles (Plate CLXXXIX., Fig. 1, and Plate 
CLXXXIX., Fig. 3, p m 4-6). 
It has four sets of constrictors, two running (Plate CXCL, 
