590 Wisconsin Academy of Sciences, Arts, and Letters. 
branous lacinia shows a weak tooth differentiated at its apex, 
which, being of no nse, seems to prove that it did form part 
of the toothed end of the mandible which has now become 
membranous. In Trichius, again, the tip of the galea becomes 
fringed at the edge. This insect thus shows, in the shape of 
its mandibles, as in its epipharynx, a resemblance to the 
Copris-beetles; but the absence of a well developed molar and 
of a conjunctivus shows that it is not closely related to them, 
belonging rather at the end of the series. 
Maxillae. These are merely accessory organs, used for 
passing the food seized by the mandibles on into the mouth, 
and also for adjusting it between the molars; acting somewhat 
like the tongue in vertebrate animals. They do not, therefore, 
show a great amount of variation, only following the mandi 
bles in a general way in the greater or smaller amount of chi- 
tinization and armature. In the pollen-eating forms they are 
clothed with long, stiff brushes. 
Labial structures. These show a very interesting series in 
development. In the Copris-beetles, the mentum is turned 
back over the sub-mentum, so that the palpigers and lobes a- 
rise from its dorsal surface. Normally the appendages arise 
from the ventral surface of the mentum, the origin of the lobes 
being in front of the palpigers; but on account of the abnormal 
relation which is here shown in the position of these parts, the 
appendages now arise from the dorsal surface; the palpigers 
are in front of the origin of the lobes. The mentum itself is 
membranous, and the lobes are comparatively distinct; the 
galea and lacinia borne by each half of the labium are fused; 
the structures formed on each side by this fusion are separate 
except at their posterior ends, at which part the hypopharynx 
arises as a distinct median organ. The hypopharynx disap¬ 
pears, its function being taken over by the posterior parts of 
the inner lobes, which begin to fuse along the median line. 
This fusion advances until the lobes form a single plate (show¬ 
ing in some cases remnants of the inner lobes as a dorsad pro¬ 
jection), and the sensory structures, representing the hypo¬ 
pharynx, disappear. This is the condition in Trox. In the 
