The nervous system is reduced to an œsophageal ring. No organs of sense are recognizable except the papillæ at the anterior end. There are neither organs of circulation nor of respiration.[355]
The sexes are distinct. In the small male the sexual orifice is situated ventrally in the anterior part of the body; in the female it is placed near the anus. The Linguatulidæ lay eggs, and from each egg, after being conveyed into an intermediate host, a four-legged larva, with rudimentary mouth parts, hatches out. It goes through a series of metamorphoses, and passes through a second larval condition, which, however, possesses the essential characteristics of the fully developed form. Sooner or later it migrates during this stage, and reaches its final host, mammal or reptile, in the nostrils or lungs of which the adult Linguatulidæ live.
[As adults they live as internal blood feeders in various birds, reptiles and mammals, especially in the nasal and respiratory passages. The larval stage occurs in another host in an encysted condition; this host is usually an animal preyed upon by the species in which the sexual forms are found. The larvæ bore through the walls of the host’s stomach and enter liver and spleen or brain, where they encyst; here they grow until they assume almost the appearance of the adult. These encysted larvæ on being eaten later make their way into the nasal passages and lungs, where they mature. Both adults and larvæ occur in man, as mentioned later.
[Three genera are recognized in this family:—
[(1) Linguatula.—Body flat, annulated. Adults live in the nasal sinus.
[(2) Porocephalus.—Body cylindrical, elongate, with often deeply cut rings. Adult in respiratory organs of snakes, larvæ in animals and man.
[(3) Reighardia.—Cylindrical, but not ringed. Not found in humans.—F. V. T.]
Genus. Linguatula, Fröhlich.
Linguatula rhinaria, Pilger, 1802.