356 ZOOLOGY 
oral appendages are at the end of a long snout. The mouth 
appendages are of the type described in Melolontha; as a rule 
the maxilliary palp is four-jointed, the labial palp three- 
jointed. 
The prothorax is well developed, the mesothorax small, 
and the metathorax of fair size. The legs are usually adapted 
for running, but in some cases they are flattened for swimming 
or strengthened for digging. The number of joints in the 
tarsus is usually four or five, but it may be smaller, and this 
variation forms the basis for grouping the various families into 
sub-orders. 
The anterior wings or elytra, when at rest, meet in a 
straight line which terminates anteriorly at a small triangular 
area of the mesothorax termed the scutellum, often invisible 
except when the wings are opened or the prothorax extended. 
In some families, as the STAPHYLINIDAE, the wings only extend 
over the anterior abdominal segments, leaving the larger part 
of the abdomen exposed. In rare cases they and the hind 
wings are absent, as in the female Lampyris. 
The elytra are in some species fused together, and the 
posterior wings are then feebly if at all developed; flight is 
therefore impossible. In the more normal forms the beetle, 
when flying, extends the elytra at right angles to the body, and 
keeps them in this position motionless (Fig. 204). 
The ventral surface of the abdomen is more strongly pro- 
tected by chitin than the dorsal, which is covered in by the 
thick elytra. The hinder segments are often invaginated, and 
form a recess connected with the openings of the generative 
organs. 
One or two genera of the ELATERIDAE, and almost all the 
LAMPYRIDAE, are provided with phosphorescent organs, usually 
in both sexes. In the males of the latter order, the light- 
giving structures shine through the ventral surface of the two 
posterior abdominal segments; in the former they are placed 
in the prothorax, and on the suture between the thorax and 
abdomen; in both cases they consist of numerous fatty cells, 
with a very rich supply of tracheae and nerves. 
Beetles usually lay their eggs in the neighbourhood of the 
food which will afford support to their larvae. The latter are 
