110 
ENTOMOLOGICAL SOCIETY 
Frc. i. Underside of Centrums biaculeatus ; I, 
II, III, IV, the coxse ; a, prosternum ; b, 
mesosternum ; c, metasternum ; d, genital 
operculum ; e , labium covered in the me- 
dian region by the prosternum ; f t jugum 
with the combs. 
families depends upon the presence of one or two minute teeth on the 
inferior margin of the immovable ringer. 
The maxillae are situated below 
the mandibles, in close proximity. 
They are broad and square and of 
a hard chitinous consistence; they 
are upholstered on their inner sur- 
face with a fleshy and softly-pubes- 
cent cushion, which rubs against 
the one on the other side, thus pro- 
ducing a vacuum which assists in 
sucking the prey ; a sharp and pow- 
erful process at the anterior end of 
the maxillae helps the other trophi 
to tear asunder the body of the vic- 
tim. The maxillae bear the large, 
five-jointed, maxillary palpus, orig- 
inally an ambulatory organ, in 
which the three tarsal joints are 
developed into a powerful prehen- 
sile organ of large dimensions. The 
hand, the former first metatarsal 
joint, with the immovable finger (2d metatarsal segment) and the movable 
finger (the former tarsus), forms thus a part constructed like the mandibles. 
It may be of some interest to you that the chela of the Arachnids differs 
from that part in the Crustaceans in that here the outer finger is movable 
while in the latter class it is the inner finger that moves. 
In the posterior area of the narrow free space between the maxillae, we 
notice a fleshy and softly pubescent piece, the ligula, which serves here as 
a palate; at its base is the minute oesophageal opening. 
Below the maxillae, and forming the floor of the oral cavity, is situated 
the labium, a thin and flat plate-like 
organ, divided in the centre longitu- 
dinally, thus forming two lobes. The 
structural character of this part has 
been hitherto strangely misunder- 
stood on account of its external ap- 
pearance from the underside ; for here 
it appears to be four-lobed, as the long 
and narrow, two-lobed prosternum is, 
in consequence of the condition of 
aggregation in the prosoma, pushed 
over the median area of the labium, 
leaving visible at each side only a 
small part of the external area (Fig i ? 
a, the prosternum ; e, the labium). But in examining the labium from the 
FIG. -2 Part of the underside of Hormurus 
n. sp., showing distinctly the insertion of 
the coxae II (those of the first pair of true 
legs) into the prosternum; b, mesoster- 
num; c, metasternum. 
