Mr Masterman makes some interesting remarks on the chigo, or sand-flea
(Pulex penetrans). It is very minute, not exceeding one twenty-fifth of
an inch in length. It burrows between the cuticle and true skin, and
there lays its eggs--producing a swelling containing a bluish white sac,
about the tenth of an inch in diameter, filled with them. This sac is
the developed abdomen of the flea. It preserves its vitality after the
death of the rest of the parent; and when that event takes place, the
eggs are mere germs, which would ordinarily perish at the same time.
Its cutting apparatus consists of two scimitar-shaped lancets, placed in
a common sheath, with which it slices out a place beneath the skin,
large enough to bury it entirely, anchors itself firmly with its hooked
proboscis, and in a day or two dies. The abdominal section, however,
still lives, absorbing nutritive material through its walls, and growing
rapidly at the expense of the serum poured out by the irritated skin
into which it is inserted. It increases in thickness as well as in
diameter, and the eggs which now fill it grow also,--when mature, each
being half as large as a perfect flea. Thus it is seen why the
sand-flea cannot deposit its eggs as do the rest of the family.
Probably it has no more food than it carries away within itself on
quitting the egg, and therefore cannot provide the material for its
greater development. Not only men and children, but dogs, suffer
greatly from them--the latter almost tearing their feet to pieces in
biting them out, and often getting them in their lips and outer
nostrils, from which they cannot dislodge them.