Beetles 
247 
It would be reasonable to expect to find the insects of an order so pursued 
by collectors susceptible of ready classifying and determining. On the 
contrary, no order presents more difficulty to the elementary and even 
labial palpi 
■maxillary palpi 
labium - 
compound 
antenna 
''prothorax 
.mesothorax 
metathorax 
coxa- - 
trochanter- 
' 
tarsal segments 
.abdomen 
Fig. 338.—Ventral aspect of male great water-scavenger beetle, Hydrophilus sp. 
(Three times natural size.) 
advanced students of systematic entomology. The tables and keys pre¬ 
pared by the few specialists really competent to determine accurately the 
different species of beetles are as nearly impossible to the amateur and 
elementary student as any “keys” in all the field of classific entomology. 
