138 Transactions of the Royal Microscopical Society. 
complex than, the mandibles. Commencing from the base, the hinge 
( cardo ), Plate CXCII., Fig. 7, e, is a short, transverse, chitinous 
rod, somewhat expanded at both ends, if seen from the sides, but if 
seen in front it is shaped more or less like a racket. It articulates 
with the stem of the organ, by a short, small, intermediate piece. 
The stem of the organ is elongated, and bears a few scattered 
hairs. The base only of the stem is shown in Plate CXCII., Fig. 7. 
The next segment is so much expanded on its inner side, that 
it and the following segments almost seem to lie transversely and 
side by side at the free end of the stem. The inner edge has a 
row of fine spines. The terminal segment is setose at the extre- 
mity, and moreover has a longitudinal row of palisade-like hairs, 
very closely apposed, and indeed almost touching one another. 
Diverging from their upper end there is a row of papillae. 
The palpus (Plate CLXXXIX., Figs. 1 and 2 m p) is six-jointed. 
The segments are elongated, the basal is somewhat shorter than 
the second and third ; the fourth is about as long as the first, 
while the two apical are again rather shorter. 
The maxilla of F. rufa very much resembles that of L. fiavus. 
That of Polyeryus rufescens is smaller in proportion, but the 
principal difference consists in the fact that the palpus is only 
four-jointed, as is also the case in Atta harbara ; while in other 
species, as, for instance, according to Westwood, in Pheidole pro- 
videris and Typlilopone fulva, there are only two segments. 
The labium, or lower lip, is also very complex. It is firmly 
attached to the maxilla. The basal portion (mentum of Meinert) 
is compressed laterally, and strengthened by chitinous ridges. At 
the upper side of the free end are two lobes, known as the para- 
glossrn, at the base of each of which is a row of rod-like hairs, 
shaped much like marrow spoons. On the under side rise the 
labial palpi (Plate CLXXXIX., Figs. 1 and 2 L P), which in 
Lasius and Formica are four-jointed. Between the paraglossas and 
the palpi is a hemispherical cushion, the lingua (Plate CLXXXIX., 
Fig. 1 , L), which shows a beautiful and very complex system of 
projecting chitinous ridges, which perhaps serve to raise up the 
fluid nourishment into the mouth. Between the last of these 
ridges and the paraglossse is a row of fine orifices. At the extre- 
mity of the lingua are two small leaf-shaped laminae. 
The lower lips of Polyeryus rufescens and of Atta harbara are 
constructed on a very similar plan, but the segments of the labial 
palpi, like those of the maxillary, are diminished in number, being 
reduced to three in Atta harbara, and two in other species, as, for 
instance, Polyeryus rufescens, Atta cephalotes, Pheidole providens, 
Typhlopone fulva, &c. In Atta moreover, the ridges of the lingua 
appear to be less projecting than in the other species. 
Passing now to the muscular system, the largest muscles in the 
