i6S 
INSECTS. 
when it becomes vitiated can be squirted out again either gently or with con¬ 
siderable force. When it is suddenly and violently expelled, it serves to propel 
the insect forwards at a rapid rate. The larvae live about ten or twelve 
months, during which time they undergo several moults; rudiments of wings 
appearing some time before the final transformation. When this is about to 
take place, the larva leaves the water by climbing the stem of a plant, or to 
some other dry spot. As the time approaches, its eyes, which were before dull 
and opaque, become bright and transparent. Its skin dries up, and soon begins 
to crack along the middle of the thorax; the thorax appears through the cleft, 
and swelling up causes it to extend ; the head is next disengaged, and the legs 
are then drawn out of their sheath. The insect now throws its head farther 
and farther back, and by this means gradually frees the hinder part of its 
body, with the exception of the last few segments which still remain enclosed in 
the larval skin. After a while, it suddenly bends its body forwards, grasps the 
12 3 4 5 
LIFE-HISTORY OF DRAGON-FLIES. 
1, Larval skin of a dragon-fly ; 2, Larva with its mask exserted ; 3, Libellula depressa ; 4, Advanced larva 
of a libellula ; 5, The same about to undergo its final transformation. 
sides of the sheath with its legs, and, doubling up its abdomen, finally extricates the 
rest of its body. 
Dragon-flies are divided into three families, of which the first two have more 
in common with one another than with the third. The Libellulidce are dis¬ 
tinguished by their, comparatively stout bodies; by the size of their eyes, which 
cover almost all the sides of the head, and very nearly meet on its crown; and 
by the structure of their lower lip, in which the median terminal piece is short 
and slightly divided at the end, while the very broad palps spread out and overlap 
it in front. The last character is useful in distinguishing the Libellulidce from the 
next family, which in many respects they resemble. Their larvae breathe by 
means of internal gills, and have a mask which is hollowed out on the inner side, 
and somewhat resembles a helmet. Members of this family are found in most 
parts of the world, and about twenty species occur in Europe. The SEsclinidce 
have eyes even larger than those of the Libellulidce. The end piece (ligula) 
