The Flea

were mentioned. These most interesting parts of the insect must now be dealt with. The reader probably knows that some insects have mouths for su

and the minute accuracy of whose observations still often fills modern naturalists with wonder. Microscopic work was then in its early days, but Leeuwenhoek clearly made out the two serrate

he parts have been mastered, a diagram will make their relative positions clear. It may be necessary, first, to remind the reader who is not an entomologist that the real mouth of an insect is the entrance to the alimentary canal, and that the appendages of the mouth, which act like jaws for masticating or like

n of segments each bearing a pair of jointed appendages. Insects of the present day never have more than six legs, but t

labium and labial palpi, the mandibles and the labrum. The labrum is considered by some authorities to be the

ot serve for piercing or sucking, and appear to have no active function unless they serve to separate the hairs of the host and enable the flea to reach the bare skin. In the majority of bat-fleas (Ceratopsyllid?) th

They spring from the base of each of the maxill? where these latter organs are joined to the head of the flea. The palpi are sense-o

of the mouth. It may be described as the lower lip of the flea. At its end it divides into two comparatively long branches. These are the labial palpi.

of five segments. This appears to have been the original state of things in the ancestral flea; the palpus with more and the palpus with less segments being derived from the normal five-jointed one. The rostrum of a flea is not a piercing organ like that of a fly and a bug. The two labial palpi separate and lie flat, right and left, on the skin when the true piercing organ is driven i

e like those at the apex of the maxillary palpus. When a hungry flea is put on one's ar

ith serrated edges. They make the puncture and are

e upper lip of the flea. It is a hard, sharp, awl-like instrument: in shape like a horny troug

e relative positions of the m

edges. The four-jointed hairy maxillary palpus is below, only one being shown. Protruding from the base of the face is the labium which supports the j

In doing this, it uses its own weight and the strength of the foremost and middle pairs of legs. The hind pair of legs are lifted up into the air. The head can soon be seen coming nearer the skin. The rostrum then divides in the middle. The labial palpi are forced apart as the mandibles and labrum penetrate into the victim's flesh. Finally, they are driven entirely asunder and lie flat on the skin of the host, one to the right and the other to the left. The flea then satisfies its hunger. A stream of blood is sucked up, and when the meal is over, there is a forcible action of the legs and t

rvous cord running from it down the backbone, and a number of nerves issuing, from the spinal cord and from the brain, in various directions. Here the main nervous system runs down the back of the animal. In a flea, or other insect, the nervous system consists of a chain of ganglia connected by a nervous cord. A ganglion is a nerve centre and, in a sense, each is a brain which may be likened to the one brain of the vertebrate. We have in the cord of ganglia a series of brains, as it were, running from the head down to the extremity of the abdomen.

us system lies on the floor of the body under the digestive canal of the flea, whereas in the vertebrate it lies along t

glion above the gullet. In bees and some other insects it has been shown that the nerves from the palpi and mouth-parts go to the next ganglion which is beneath the gullet. The same is

the brain are completely atrophied. Whether this is so in the

uded from the head. The versatile basal segments and the terminal c

nn? groove. Just as many of the older naturalists thought that the maxillary palpi were antenn?, so others thought that the antenn? of a flea were its ears. And when, with the help of their lenses, they saw the antenn? erected and protruded from their grooves, they imagined that the insect was cocking its ears and listening after the manner of a horse or ass. But the antenn? of fleas are much more to them than ears; though it may be that they are also auditory organs. They are certainly tactile and olfactory organs as well. In outward structure each antenna consists of two parts which may be called the stalk and the club. The club is divided into a number of segments and is plentifully supplied with hairs. In some species the cuts which divide t

of the male are usually raised and exposed from the groove. Insects generally have some means of cleansing dirt from their antenn?. Some make use of their legs, others of their mouth-parts. In fleas there is often a row of short hairs at the hind margin of the groove which may serve as a kind of comb for cleaning these delicate o

base by a ring. Somewhat similar sense-organs are widely spread through the insect world. As to their function, divergent views are held. Some think that they are for the perception of sounds, some for the perception

omed host, lead one to believe that they have a sense of taste. This sense in other insects is apparently seated in certain microscopic pi

ove. This is most marked in the genus of African fleas Listropsylla. The real nature of this organ is unknown. Some regard it as an organ of sense. Its homology is also uncertain. To some it suggest

supplied with hairs and nerves and always placed on the back of the ninth abdominal segment. Of all its uses we are still somew

The frontispiece represents a male flea and shows this well. The internal organs of reproduction (testes and ovaries) in the male and female are placed near the end of the abdomen. The seminal outlet and common oviduct open to the rear of the sensory p

ments which are altered. In the females the eighth, and also often a portion of the seventh, has assumed a peculiar shape. The clasping organs of the male flea are portions of

recognise the species when other organs do not show sufficiently striking characters. A minute study of the genitalia of fleas is an absolute necessity to the systematic entomologist, th