THE SUBSTITUTE. 
139 
NEW BOOKS. 
Dallas’s ‘ Elements of Ento- 
mology.’ 
We continue tlie extracts we 
commenced at p. 70. 
WATER BEETLES. 
“ One of the larpjest, most for- 
midable and most abundant of the 
British species of this group, is the 
Dyticns marginalise or Margined 
Water Beetle, specimens of which 
may be obtained in almost any 
piece of water. This insect mea- 
sures from an inch to an inch and 
a quarter in length, and is of a 
broad oval form ; the whole upper 
surlace is blackish olive, except 
the margins of the prothorax, and 
the outer margins of the elytra, 
which are of a dull yellow colour, 
as is also the lower surface of the 
body. The whole structure of this 
insect is admirably adapted to its 
aquatic residence; its thorax is as 
wide at the base as the elytra, so 
that iis form is a complete oval ; 
its body is thickest in front, and 
there is not a projection of any 
kind from its surface to impede its 
motion through the water. The 
liindlegs form a pair of long, broad 
and powerful paddles, the surface 
of which is increased by a fringe 
of stiff hairs running down the 
inner margin of the flattened tarsi, 
and by the action of these the Dy- 
ticus is enabled to swim through 
the water at a rapid rate. But 
although thus fitted for an aquatic 
life, the beetle is nevertheless under 
the necessity of rising fretiuently 
to the surface for a stipply of air, 
and this operation is effected in a 
very simple fashion. It is to be 
borne in mind that the body of the 
insect is considerably lighter than 
water, and that he only keeps him- 
self below the surface by the rowing 
action of his powerful limbs. Ac- 
cordingly, when he finds it neces- 
sary to breathe, he simply suspends 
the w'orking of his paddles, when 
his body gradually rises to the sur- 
face, but as the fore part of it is 
thicker and heavier than the rest, 
it naturally remains immersed in 
the water, when his tail is exposed 
to the air. This is the very 
arrangement he requires, for his 
respiration being effected through 
a pair of stigmata, which are con- 
cealed beneath the elytra at the 
extremity of the abdomen, he has 
nothing to do after rising to the 
surface but to raise his elytra a 
little, take in his fresh cargo of air, 
and then go off about his business. 
This consists, for the most part, in 
the pursuit and slaughter of all his 
weaker neighbours, which he seizes 
remorselessly with his fore-feet, and 
conveys to his mouth w iih great re- 
lish. Anacreon has written ope or 
two odes on the supposed happiness 
of the Cicada, which, if we may 
judge from the noise made by that 
insect, must be very great indeed. 
However, on a careful comparison 
of the circumstances of the two in- 
sects, I can’t help thinking that the 
balance of comfort, at any rate, 
must be in favour of our friend 
the water beetle. There he is this 
awfully hot day, when we, who 
have walked out to look at him, 
are in a most miserable state of 
perspiration, — there he is enjoying 
the luxury of a cool bath, with every 
necessary of his existence within 
easy reach, — his food to be had 
without any more exertion than 
just what has been recommended 
by the wisest men in all ages, to 
