86 
BRITISH BEETLES. 
ment, being the terminations of two great lateral 
tracheal tubes, through which the insect breathes. 
These larvae are very voracious, feeding on other 
insects, &c. ; they swim well, bending themselves into 
an arch, and often placing the head backwards on to 
the body : when handled, they become flaccid, and 
emit a fetid black fluid from the end of the abdomen. 
The pupa is formed in a cell in the wet earth of the 
banks of ponds. 
A smaller species, Hydrobius fuscipes (Plate VII., 
Fig. 5), is very common in stagnant waters. 
There is perhaps no group of Coleoptera in which 
the members vary so much in size : thus Hydropkilus 
piceus is sometimes nearly two inches long, whereas 
the tiny IAmnebius picinus, which almost resembles 
the last-named species in miniature, does not measure 
one line ; the species of Hydrochus are distinguished 
by their elongate form and prominent eyes ; one or 
two of them have the interstices of the elytra rather 
strongly raised ; the Berosi are dirty-brown or testa- 
ceous insects with the disc of the thorax metallic ; 
they are better swimmers than most of their allies, 
and by the movement of their abdomen are able to 
produce a rather strong stridulation ; their larvae are 
very peculiar, by reason of the very long branchial 
appendages borne by the first seven abdominal seg- 
ments : the little shining-black globular Chsetarthria 
seminulum is perhaps the only other member of the 
section worth mention ; it is found in damp moss, and 
is remarkable for having the first and second ventral 
segments of the abdomen covered by two plates meet- 
ing in the middle. 
The SruiERiDiiNiE are mostly terrestrial in their 
