CHAPTER XII. 
THE APHANIPTERA. — THE STREPSIPTERA. 
The Aphaniptera are insects which are known to everybody; but 
the Strepsiptera have never been seen except by a few naturalists. 
The first are Fleas, and are admitted to be particularly interesting 
insects, quite as much as regards their structures, their instincts, 
and metamorphoses, as on account of their well-known habits. 
The adult fleas are suckers, like the Hemiptera, but their mouths 
are constructed very differently, for the lip is a sharp tissue ; the 
mandibles are long flattened blades finely denticulated on their 
margins ; the jaws are small triangular pieces ; and the lower lip 
is a membranous lamina supporting large palpi. The eyes are 
situated on the sides of the head, and appear to be simple ; the 
antennae are very small, and the wings only exist in the form of 
scales, as small vestiges of those important organs — hence the name 
of Aphaniptera. The legs are strong and spiny, and the hind ones, 
which are longer than the others, have their thigh pieces enlarged, 
and are admirably suited for jumping. These insects undergo 
complete metamorphoses, and the larvae are worm-shaped, and the 
nymphs are inactive, but the last transformation is imperfect, for 
the organs of flight are rudimentary. There is only one family in 
this order, and it has only one genus, that of the fleas (. Pulex ). 
Each species attacks one animal in particular, and one kind selects 
man as the object of its attentions. This last is readily recognised 
by its smooth head, and by the stiff hairs upon the segments of 
the thorax and the abdomen. 
It is not necessary to explain how fleas live ; they multiply 
prodigiously in hot climates, and grow to a very unusual size 
under certain conditions. For instance, immense fleas, which are 
