. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. TRICHINA, HOOKWORMS, FILARIA, ETC. 85 ment these larval forms must be taken into the alimentary canal of a mosquito. There they undergo certain changes, and then make their way through the walls of the stomach into the muscles, where they increase in size until they are about one-sixteenth of an inch in length. Later they migrate to other parts of the body, some of them to the proboscis of the mosquito from wrhich they issue when the mosquito is feeding and thus gain entrance into another host. It is not known tha
. Elementary textbook of economic zoology and entomology. Zoology; Insect pests. TRICHINA, HOOKWORMS, FILARIA, ETC. 85 ment these larval forms must be taken into the alimentary canal of a mosquito. There they undergo certain changes, and then make their way through the walls of the stomach into the muscles, where they increase in size until they are about one-sixteenth of an inch in length. Later they migrate to other parts of the body, some of them to the proboscis of the mosquito from wrhich they issue when the mosquito is feeding and thus gain entrance into another host. It is not known that these parasites can gain an entrance into the circulatory system in any other way, but it has been suggested that mosqui- tos dying in the water may liberate some of the filariae which may later find their way into the vertebrate host when the water is used for drinking. Soon after entering the circulatory system of the human host the parasites make their way into the lymphatics where they attain sexual maturity, and in due time new generations of FIG. 29.—Microfilaria ,v i i £i • r-i of the blood; immature the larval filariae, or microfilanae, are stage of Fila'ria bancroflL poured into the lymph, and finally (Greatly enlarged; after into the definite blood-vessels, ready Terzi-) to be sucked up by the next mosquito that feeds on the patient. In most cases of infection the presence of these filariae in the blood seems to cause no inconvenience to the host. They are probably never injurious in the larval stage, that is, in the stage in which they are found in the peripheral circulation. In many cases, however, the presence of the sexual forms in the lymphatics may cause serious complications. The most common of these is that hideous and loathsome disease known as elephantiasis, in which certain parts of the patient become greatly swollen and distorted. An arm or a leg may become swollen to several times its natural size, or other parts of the body may be seriously affect
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