The Animal Parasites of Man

Section I.--Club of Antennæ Distinctly Segmented Only on the Hind

side.

Key to Genera.

a. No comb on head and thorax.

a^1. The internal incrassation, which extends from the insertion of the mid coxa into the thorax, joins the anterior edge of the mesosternite Pulex.

b^1. This incrassation joins the upper edge of the mesosternite Xenopsylla.

b. With a comb on the pronotum only Hoplopsyllus.

c. With a comb on the pronotum and at the lower edge of the head Ctenocephalus.

Section Ii.--Club of Antennæ Distinctly Segmented All Round.

Key to Genera.

a. Eye developed.

a^1. No comb on head.

a^2. Pygidium not projecting backwards; frons with tubercle Ceratophyllus.

b^2. Pygidium strongly convex, projecting backwards; frons without tubercle Pygiopsylla.

b^1. Two spines at angle of genæ Chiastopsylla.

b. Eye vestigial or absent.

a^1. Abdomen without comb.

a^2. Hind edge of tibiæ with about eight short and several long bristles, which do not form a comb.

a^3. Fifth segment in fore and mid tarsi with five, and in hind tarsus with four bristles Neopsylla.

b^3. Fifth segment in fore and mid tarsi with four, and in hind tarsus with three lateral bristles, there being an additional pair of bristles in all the tarsi on the ventral surface in between the first pair Ctenophthalmus.

b^2. Hind edge of tibiæ with about twelve short and three long bristles, the short ones forming a kind of comb Ctenopsylla.

b^1. Abdomen with at least one comb Hystricopsylla.

Genus. *Pulex*, Linn.

*Pulex irritans*, L., 1758.

Male 2 to 2·5 mm. in length, females about 4 mm.; reddish or dark brown; head without bristles; thoracic and abdominal rings of bristles on the dorsal aspect, and small hairs directed backwards at the posterior margin. The barrel-shaped white eggs are deposited in cracks in the boards, sweepings, spittoons, etc.; they produce legless larvæ consisting of fourteen segments, which, after about eleven days, are transformed into pupæ; after another eleven days the flea emerges.

Fleas live in human dwellings all over the world, and periodically pass on to persons to suck their blood. They may deposit their eggs on very uncleanly individuals, and even undergo development, therefore it is possible to find larvæ and pupæ on such persons.

The dog flea, Pulex serraticeps, is easily distinguished from the flea of man by the large thick bristles on the posterior margin of the first thoracic ring (fig. 384).

Genus. *Xenopsylla*, Glink.

*Xenopsylla cheopis*, Rothschild.

This is the common rat flea of tropical countries. Rothschild says: “Although practically cosmopolitan, it cannot apparently flourish in temperate and cold climates.”

Bull. Ent. Res., 1911, i, pt. 2, p. 92.

In the male the bristles of the flap-like process of the clasper all slender; in the female the narrow portion of the receptaculum seminis long. Originally discovered in Egypt.

This is apparently the chief plague flea. The Indian Plague Committee have proved that this flea is easily infected when fed on plague rats, and that the bacillus multiplies rapidly in the flea’s stomach and that the fleas may remain infective for fifteen days. How the flea infects man does not apparently seem to have been proved, as it does not do so through its bite, but the excrement is highly infective. It is probable that this poisoned fæcal matter gets to the wound caused by the piercing mouth.

*Xenopsylla brasiliensis*, Baker,

occurs on rats in West Africa and has been introduced into Brazil.

Genus. *Ctenocephalus*, Kolen.

Includes the cat and dog fleas. The dog flea, C. canis, Dugès, is found on the dog all over the world, but especially in temperate climates. It also occurs on rats. Man is often badly bitten by this insect and it overruns houses. The eggs are laid on rugs, carpets and dust and dirt and amongst dogs’ hair, but are not fastened to it and fall anywhere. The ova may hatch in about fifty hours and the larvæ live for seven days and then spin their cocoons amongst dust and dirt. The pupal stage lasts about eight days.

The cat flea (C. felis) is widely distributed over the world, and occurs on many mammals beyond the cat, and is also found on rats.

Genus. *Hoplopsyllus*, Baker.

A genus found in North America related to Pulex, but at once recognized by the prothorax bearing a comb.

*Hoplopsyllus anomalus*, Baker,

which is found on the ground squirrel (Citellus beecheyi) in California, and according to Rothschild once found on the rat, has been proved to carry the plague bacillus and to play an important part in plague infection in California.

“Report United States Public Health, 1909,” xxiv, No. 29.

Genus. *Ceratophyllus*, Centis.

*Ceratophyllus fasciatus*, Bosc.

This flea is also found on the rat in Europe and will attack man. It is a plague carrier. It has eighteen to twenty teeth on the prothoracic comb and no black spines on the head. The genus Ceratophyllus of Centis has a pronotal comb and three ante-pygidial chætæ on each side. Two other specimens recorded: C. londiniensis, Rothsch., and C. anisus, Rothsch. The former on rats and mice in London, the latter on Felis sp. from Japan and Mus norvegicus in California.

Genus. *Ctenopsylla*, Kolen.

This genus contains a very abundant rat and mouse species, C. musculi, Dugès, which is widely distributed over the globe.

Genus. *Hystrichopsylla*, Tasch.

Large hairy fleas, with no eyes and one or more combs on the abdomen. In the Mediterranean area one species, H. tripectinata, Tirah, is common on rats and mice, and also in the Azores. Several others occur on rats and mice. For information concerning these the reader is referred to Rothschild’s papers.

*Pulex pallipes* is another species found on the rat and man.

*Systematic, Anatomical, and Biological Remarks on Mosquitoes.*

Mosquitoes come in the Nematocera, one of the sub-orders of the Diptera, and are divided into numerous families, of which, however, the Culicidæ are of most interest to us here. Other families as the Psychodidæ and Chironomidæ are also of considerable importance, vide following pages. The head is small, the facetted eyes are placed laterally, but there are no accessory eyes (ocelli). In front of the eyes are situated the comparatively long antennæ, the differences of which strongly mark the distinction of sex.

The antennæ are composed of fifteen or sixteen segments. In the male they are covered with long whorl-like hairs, while in the female the antennal hairs are short--differences that are perceptible even with the naked eye. The proboscis, which is longer than the antennæ, protrudes from the inferior aspect of the head and is composed of the following parts (figs. 387 and 388): Two grooved half tubes, facing one another, of which the upper one is the upper lip (labrum) and the lower one the lower lip (labium), which represents a pair of coalesced maxillæ. Within the tube formed by the labrum and labium are the mandibles and maxillæ, transformed into instruments for piercing, and a single puncturing organ, the hypopharynx. On the right and left, next to the proboscis, are placed the straight five-jointed palpi, the final joint of which is thickened in the male. In biting, the labrum, which is swollen at its free end, is not introduced into the wound like the other mouth parts, but is bent backwards. The labium and hypopharynx push direct into the skin; the maxillæ and mandibles, however, which are needle-like and serrated at the tips, penetrate with a saw-like movement. [The swollen free end of the labrum really means the labellæ, two articulated pieces, supposed by some to be the labial palpi. In most species the mandibles are not serrated at their ends.--F. V. T.] The saliva is introduced into the wound through the lumen of the hypopharynx, while the blood is sucked up by the mosquito in the groove of the labium.

The three thoracic segments are soldered together. The central one carries the membranous wings on the sides of the dorsal surface; the posterior somite carries the small halteres (rudimentary posterior wings). There are three pairs of long slender legs on the lower side.

† [This should read Anopheles maculipennis, Meig.; there was no type of A. claviger.--F. V. T.]

The abdomen has no limbs, is composed of eight (rarely nine) distinct segments; the sexual and anal orifices are at the posterior end, the stigmata on the sides. The intestinal canal (fig. 389) is composed of three principal divisions; the anterior part reaches as far as the front pair of legs, and consists of the œsophagus, which is provided with two small lateral diverticula. [At the commencement of the œsophagus are one or more diverticula, which vary in size; they contain air, food and bacteria.--F. V. T.] The mid gut reaches as far as the fifth and sixth abdominal ring; in front it is thin, and has numerous small supra-œsophageal ganglia; the posterior part is, however, more dilated. Four or five Malpighian tubes, the excretory organs, discharge at the place where the mid gut passes into the terminal gut.

The pair of salivary glands have one common excretory duct leading into the hypopharynx.

These glandular bodies are situated in the thorax; each consists of three slightly serpentine tubules, the dorsal and ventral tubes being long, the central one shorter. The above-named characteristics apply to both genera Culex and Anopheles, but in the genus Culex is smaller, Anopheles larger. [In Anopheles the ends of the ducts in the lobules are dilated, whilst in most of the genera the ducts are the same size all along. The lobules may bifurcate, and in Psorophora there are five lobules.--F. V. T.] The legs of the genus Culex are about the same length as the whole body; in Anopheles they are double that length. In Anopheles the palpi and proboscis are of equal length; in Culex the condition is different, according to sex. In the male the palpi are longer than the proboscis; in the female considerably shorter and the number of segments diminished. The venation of the wings exhibits further points of differentiation, as also their adornment, though this last sign is not by any means always conclusive; most species of the genus Culex have unspotted wings, whilst those of Anopheles are usually spotted. More important is the fact that in Culex the abdomen is decorated with small scales, similar to those on butterflies, whereas there are small bristles on the abdomen of Anopheles. [This cannot be said to be a character by which an Anopheline may be told from a Culicine, for in such common Anopheline genera as Cellia and Neocellia we get plenty of scales on the abdomen.--F. V. T.] An experienced observer can, however, separate the two genera by the difference in size and their manner of resting. When settled they either touch the resting place with all the legs or only with the four anterior legs. In consequence of the different length of the legs, the body of Culex approaches the resting place more closely; moreover, Culex holds the abdomen parallel or at an acute angle to the resting surface, whereas Anopheles carries the abdomen directed upwards (at an angle of about 145°) and holds the head down. Both genera, however, usually only rest on the four anterior legs, and then, as has long been known, Culex carries the third pair directed towards the dorsum, while those of Anopheles hang down.

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