Hardenberg—Studies in the Trophi of the Scarabaeidae . 591 
leaf-chafers appears a new displacement of the mentum; it io 
at first pushed slightly inward over the sub-mentum, a condi¬ 
tion which later becomes more pronounced. This movement 
may continue so far that in extreme cases the mentum is en¬ 
tirely pushed inward and the sub-mentum projects in front. 
The hypopharynx has now entirely disappeared, and the men¬ 
tum consists of one plate formed by the fusion of the labial 
lobes and the mentum proper. The palpigers and palpi arise 
from its ventral surface, between the mentum and the sub- 
mentum. The front and lateral edges of the mentum become 
chitinized and are turned inward, forming a structure similar 
to that found in the epipharynx. The lateral edges of the sub- 
mentum are curved inward and joined to the edges of the men¬ 
tum. Lastly, the anterior edge of the sub-mentum fuses with 
the mentum where this overlaps it, and at this stage only a 
lateral view of the structures shows the true state of affairs. 
These are the conditions in the leaf-chafers. 
In the flower-beetles the sense of taste shows a greater de¬ 
velopment, and, although the members of this group approach 
in their epipharyngeal structure to the Copris type, their la¬ 
bial structures remain in their relative position practically un¬ 
changed. FTo hypopharynx is developed, but taste-cups ap¬ 
pear on the inner surface of the labium. 
The sub-mentum also shows a progressive series of changes. 
When in the Coprini both plates are distinct, the anterior is 
smaller than the posterior. This difference in size becomes 
less pronounced, until at the beginning of the leaf-chafer series 
both plates are of equal size. From this point on the anterior 
plate increases in size, so that in the flower-beetles the original 
conditions are reversed and the anterior plate is large, taper¬ 
ing toward its distal end, while the posterior plate forms a 
small transverse sclerite between it and the gula. 
Zoological Laboratory, University of 
Wisconsin , June 1905 . 
