c. Legs usually well developed, body more or less depressed (fig. 49). Mites ACARINA cc. Legs stumpy or absent, body more or less elongate or vermiform, or if shorter, the species is aquatic or semi-aquatic in habit. d. Four pairs of short legs; species inhabiting moss or water. Water-bears. TARDIGRADA dd. Two pairs of clasping organs near the mouth, instead of legs, in the adult; worm-like creatures parasitic within the nasal passages, lungs, etc. of mammals and reptiles (fig. 148). Tongue worms. LINGUATULINA [Illustration: 148. Linguatula. (_a_) larva; (enlarged). (_b_) adult; (natural size).] ACARINA[E] a. Abdomen annulate, elongate; very minute forms, often with but four legs (fig. 62). DEMODICOIDEA b. With but four legs of five segments each. Living on plants, often forming galls. ERIOPHYIDÆ bb. With eight legs, of three segments each. Living in the skin of mammals. DEMODICIDÆ To this family belongs the genus DEMODEX found in the sebaceous glands and hair follicles of various mammals, including man. _D. phylloides_ Csokor has been found in Canada on swine, causing white tubercles on the skin. _D. bovis_ Stiles has been reported from the United States on cattle, upon the skin of which they form swellings. D. FOLLICULORUM Simon is the species found on man. See page 78. aa. Abdomen not annulate nor prolonged behind; eight legs in the adult stage. b. With a distinct spiracle upon a stigmal plate on each side of the body (usually ventral) above the third or fourth coxæ or a little behind (fig. 50); palpi free; skin often coriaceous or leathery; tarsi often with a sucker. c. Hypostome large (fig. 50), furnished below with many recurved teeth; venter with furrows, skin leathery; large forms, usually parasitic. IXODOIDEA d. Without scutum but covered by a more or less uniform leathery integument; festoons absent; coxæ unarmed, tarsi without ventral spurs; pulvilli absent or vestigial in the adults; palpi cylindrical; sexual dimorphism slight. ARGASIDÆ e. Body flattened, oval or rounded, with a distinct flattened margin differing in structure from the general integument; this margin gives the body a sharp edge which is not entirely obliterated even when the tick is full fed. Capitulum (in adults and nymphs) entirely invisible dorsally, distant in the adult by about its own length from the anterior border. Eyes absent. ARGUS Latr. f. Body oblong; margin with quadrangular cells; anterior tibiæ and metatarsi each about three times as long as broad. On poultry, southwest United States. A. PERSICUS MINIATUS