142 INSECTS AFFECTING DOMESTIC ANIMALS. 
and must ordinarily be scattered in places where the host forms sleep 
or nest. The larvee, so far as known, live in dust or litter in similar 
locations. They are slender, worm-like, footless objects, with a sparse 
covering of hairs. The pup form in similar locations, inclosing them- 
selves in cocoons. Westwood says 
When full grown, which occurs in summer in about twelve days, the larve inclose 
themselves in a small cocoon of silk, often covered with dust, and attached to sur- 
rounding substances. Rdosel, however, observed that some of the larve underwent 
their transformations without forming any cocoon. 
In most of the available works the group is made to contain but a 
Single family, the Pulicidse, but more recent systematic works sepa- 
rate them into three families, the Sarcopsyllide, including the small 
forms, with large heads, which are confined to the host animal while in 
the gravid condition; the Vermipsyllide, in which the gravid females 
are not stationary, but the abdomen becomes swollen, and in which the 
labial palpi are 10-jointed; and the Pulicide, including most of our 
common forms, in which the female abdomen does not become swollen, 
and the labial palpi are from 3 to 5 jointed. 
While the fleas are essentially parasitic in the adult stages, they are 
by no means so strictly confined to the host as are the Pediculidz or 
most of the Mallophaga, but wander from the host at times, and may 
-even be found on different species of animals than those which are evi- 
dently their normal hosts. Probably these stragglers do not, as a rule, 
maintain a permanent habitat upon the new host, and therefore, with 
the exception of one or two species, little attention need be given to 
prevention of migration or of transfer from one animal to another. 
In the further discussion of species, which will be limited mostly to - 
the American forms of economic interest, we will disregard these 
divisions and treat the species simply under their respective genera. 
THE JIGGER FLEA, OR CHIGOE. 
(Sarcopsylla penetrans Linn. ) 
Linneeus described this species more than a century ago (1767) under 
the name of Pulex penetrans, and it has been treated in many different 
works since that time. The various names of “ jigger,” ‘“jigger flea,” 
‘“‘chigoe,” and ‘‘chique,” applied to it in various localities, are evidently, 
in part at least, associated with its annoying habit. In distribution 1t 
covers all of tropical and subtropical America. Baker says ‘this flea 
is undoubtedly found throughout the tropical and subtropical regions 
of both hemispheres.” 
Railliet states that it was introduced into Africa about the year 1872, 
and that it has propagated there with astonishing rapidity. 
While most of the records of its injuries have been with reference to 
its occurrence on man, it is a notable pest of inferior animals, and 
doubtless occurs much more frequently as a parasite of some of these 
than of man. 
