WOOD-EATING INSECTS 



141 



when we see an ornament like the feather of a grenadier's 

 cap situated on one part of the body in one species, and 

 in a totally different part in nearly allied ones. I tried 

 in vain to discover the use of these curious brush-like 

 decorations. On the trunk of a Hving leguminous tree, 

 Petzell found a number of a very rare and handsome 

 species, the Platysternus hebraeus, which is of a broad 

 shape, coloured ochreous, but spotted and striped with 

 black, so as to resemble a domino. On the felled trunks 

 of trees, swarms of gilded-green Longicornes occurred, 

 of small size (Chrysoprasis), which looked like miniature 

 musk-beetles, and, indeed, are closely allied to those 

 well-known European insects. 



I was interested in the many small kinds ofi lignivorous 

 or wood-eating insects found at Caripi, a few observations 

 on which may be given in conclusion. It is curious to 

 observe how some small groups of insects exhibit the most 

 diversified forms and habits — one set of species being 

 adapted by their structure for one set of functions in 

 nature, and another set, very closely allied, for an op- 

 posite sphere of action. Thus the Histeridse — small 

 black beetles well known to English entomologists, most 

 of whose species are short and thick in shape and live in 

 the dung of animals — are most diversified in structure 

 and habits in the Amazons region ; nevertheless, all the 

 forms preserve in a remarkable degree the essential 

 characters of the family. One set of species live in dung ; 

 most of these are somewhat cubical in shape, the head 

 being retractable within the breastplate, as in the tortoise. 

 Another group of Histeridae are much flatter in form, 

 and live in the moist interior of palm-tree stems ; one 

 of these is a veritable colossus, the Hister maximus of 

 Linnseus. A third group (Hololeptae) are found only 

 under the bark of trees ; their heads are not retractable 

 within the breast, and their bodies are excessively de- 

 pressed, to fit them for living in narrow crevices, some 

 kinds being literally as thin as a wafer. A fourth set 

 of species (Trypanseus) form a perfect contrast to these, 

 being cylindrical in shape. They drill holes into solid 

 wood, and look like tiny animated gimlets when seen at 

 work, their pointed heads being fixed in the wood whilst 

 their smooth glossy bodies work rapidly round, so as to 

 create little streams of sawdust from the holes. Several 

 famihes of insects show similar diversities of adaptation 



