The Flea

eton. In either case the skeleton serves as an attachment for the muscles by which the animal moves itself. Everyone is familiar with the external skeleton of a lobster and can see for himself how

mediately beneath. On those parts of the body which are to the rear of the head the chitin forms a series of plates or shields which overlap one another som

le armour. It is made of a fairly solid and dense substance, but, owing to the absence of carbonate and phosphate of lime, is much lighter than the familiar external skeleton of the lobster. Chitin is a very peculiar and durable substance which r

ry large flea (Hystrichopsylla talp?) is that found on the mole. The largest known flea (Dolichopsyllus stylosus) is found on small

gress. The presence or absence, the arrangement on the body, and the size of these serve, along with other features, to distinguish different species. They seem materially to help a flea in those wriggles

s, bristles, or hairs. There is, however, no real distinction in the structure or na

An insect newly emerged from the pupa is always lighter in colour; and the difference bet

s the animal to glide with greater facility through the hairs of its host. Like other insects, a flea is readily divided into a head, a thorax, and an abdomen. The head is rounded on the top and front and shows no obvious trace of segmentation; but what is known of the development of other insects leads one to think

abits of their hosts would render eyes of little or no use. If eyes are present they are large and placed on either side of the head. Each is a simple

ind have lost their organs of sight from disuse. In their simplest condition, the eyes of the lower invertebrates only enable the creature, so far as one can judge, to distinguish light from darkness. Entomologists believe that the power of vision of ocelli is probably confined to very near objects and that this simple form of e

is not impossible that this is the vestige of a once functional eye. In one genus, however, the eye and the spine are both present. Of the fleas bel

tenn?; but unlike those of a moth, a beetle, or a grasshopper, each fits neatly into a groove at the side of the head and

er part of the head and on the thorax respectively. Analagous combs are found in

the beaver, on insects allied to bed-bugs (Polyctenes) found on bats, and on wingless flies (Nycteribia) which infest Egyptian and South American bats. The majority of the Pulicid? have one or more combs with comparatively long teeth. These combs reach their maximum development in the bat-fleas which have no less than eight. Som

bly prevents the flea slipping back as it pushes forward. Bat-fleas (Ceratopsyllid?) have lobes or flaps placed

are called genal combs and take the form shown in Fig. 2. There are also combs found on the thorax. The fossil flea (Pal?opsylla klebsi

les a true comb. The other consists merely of a number of highly chitinised bristles arranged in a row. They probably both serve the same function. Apart from their use as organs to

considerably in different species. Some fleas have what may b

g the bearer of piercing and sucking organs, which require strong muscles, the

e the head into four sections. It is possible that these correspond to

spicuous neck which is characteristic of the Diptera, or flies, is not to be found in any fleas. For this r

me fleas they would bound with ease backwards and forwards over the cross on the top of St. Paul's Cathedral. Each leg consists of four segments beautifully articulated and plentifully supplied with bristles. At the end comes the foot with five very short segments. The last segment is provided with a pair of more or less formidable claws. Fleas use their legs for leaping, for running, and for clinging to their hosts. They also use their mouth-parts for the last purpose and it is worthy of note, as we shall see later on, tha

lly developed. Next come the small trochanter and the larger femur. The tibia which is long and s

e of the ground. The claws serve as grips so as to make the most of any unevenness; and thus the insect drags itself along with surprising rapi

foot segment are freely moveable and are

aterally to the first abdominal tergite. The older naturalists jumped to the conclusion that this was the remains of a wing. The best judges have, however, formed a decided opinion that no trace o

e thorax present in all insects. It is of no special service to the fl

the legs on their abdomens, why legs should now invariably be restricted to the thorax, and why there should never be more than three pairs. In the earliest known insects which lived on th

leas, as in all holometabolous insects, that is those which pass through a complete metamorphosis, the sternite of the first abdominal segment is suppresse

flea are modified for reproductive purposes a

almost transparent. They act as extensors, retractors, flexors, elevators and depressors. The joints and hinges of the skeleton allow of considerable, but not perfect, freedom. The muscles of locomotion are partly in the thor

sects. This vexed and much debated question is still, as the older naturalists would have said, tremendum mysterium. Very little light has yet been thrown upon it, and the most divergent views have been expressed by learned and competent e

and crickets; but he has had few followers. By Fabricius and by Illiger they were treated as Hemiptera or bugs. Lameere, a Belgian, has recently expressed a decided view that fleas are really a family

d, the head of the flea is closely joined to its thorax, the three divisions of the thorax are not joined and fused, the flea is wingless, the eyes of flea

they are Lamarck, De Geer, Latreille, Kirby and Spence, MacLeay, Leach, Dugès, Bouché, van der Hoeven,

s; where ought that order to be placed? In which other order of insects must we look for the nearest relations of fleas? For a time after the accept

no points of resemblance. Dahl (1899), a German, then took up the cudgels for the fly theory. Dahl pointed out the resemblance between fleas and a group of flies ca

doptera; by Dugès between the Hymenoptera and Diptera; by Brauer between the Diptera and Coleoptera. Handlirsch thinks that

of development, would produce some facts of importance. In this hope entomologists have, to a great extent, been disappointed. There seems to be much similarity between the embryos of beet

g example of the development of a temporary larval structure and it is the only known instance of such a structure in an insect. There are no traces of eyes. T

terous than of dipterous larv?. The maxill?, or second pair of jaws, are somewhat reduced and rudimentary. The absence of eyes and of l

, chitinous, structures which prop up the body of the larva when it creeps and wriggles. There are similar props in the larv? of

tudies the mouth-parts, the true view seems to be that the mouth-parts of a flea are equally unlike those of a fly and those of a beetle. Such being the present state of our