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While engorging herself with our blood, we will examine under the microscope the mosquito's mouth. Thus massed into a single awl-like beak, the mosquito, without any apparent effort, thrusts them all except the labium into the flesh. Her hind body may be seen tilling with the red blood, until it cries quits, and the insect withdraws its sting and flies sluggishly away.
As the sharp cutting organs are thrust deeper and deeper the labium doubles back like a bow and does not enter the skin. Saliva is then poured into the wound through minute grooves in the mandibles, and the blood is sucked up into the mouth by the sucking organ which lies in the head at the base of the mouth-parts.
These are the movements which the animal executes after having first inserted the labium through a sweat-pore. It follows that when the whole instrument is exserted, we perceive a long membranous flexible tube hanging down from the labium, and along the walls of this tube the setiform mandibles and maxillæ in the shape of long narrow bands of chitine.
The most frequent position is on the pectoral surface below the true mammae and somewhat nearer the middle line, but an accessory gland has been observed on the left shoulder over the prominence of the deltoid, on the abdominal surface below the costal cartilages, above the umbilicus, in the axilla, in the groin, on the dorsal surface, on the labium majus, and on the outer aspect of the left thigh.
Hernia may be congenital or acquired, or may be single or multiple as many as five having been seen in one individual. More than two-thirds of cases of rupture suffer from inguinal hernia In the oblique form of inguinal hernia the abdominal contents descend along the inguinal canal to the outer side of the epigastric artery, and enter the scrotum in the male, and the labium majus in the female.
The labium, which is the largest and most conspicuous, is apparently cylindrical but is grooved above throughout its length. At the tip of the labium are the labellæ, two little lobes which serve to guide the piercing organs. Lying in this groove along the upper side of the labium are six very fine, sharp-pointed needles.
A study of the structure and habits of fleas shows that in many respects they are particularly adapted for spreading such a disease as bubonic plague. The piercing proboscis consists of three long needle-like organs, the epipharynx and mandibles, and a lower lip or labium. The mandibles have the sides serrate like a two-edged saw.
The hypopharynx is united to the labium, the mandibles are wanting and the maxillæ are very much reduced so that the insect is unable to pierce the tough skin of animals. The male feeds on the juices of plants as do the females when they cannot get blood. It is not at all necessary for mosquitoes to have the warm blood of man or other animals. Comparatively few of them ever taste blood.
The labium is much as in that of Perla, being broad and short, with a distinct median suture, indicating its former separation in embryonic life into a pair of appendages. The labial palpi are three-jointed, the joints being broad, and in life directed backwards instead of forwards as in the higher insects. There are five American species of the genus Lepisma in the Museum of the Peabody Academy.
More than any other part of the sexual apparatus in either sex, the lesser lips, on account of their shape, their position, and their structure, are capable of acquired modifications, more especially hypertrophy and elongation. By stretching, it is stated, a labium can be doubled in its dimensions.
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