Syn.: Cercomonas intestinalis, Lambl, 1859 (nec 1875); Hexamitus duodenalis, Davaine, 1875; Dimorphus muris, Grassi, 1879; Megastoma entericum, Grassi, 1881; Megastoma intestinale, R. Blanch., 1886; Lamblia duodenalis, Stiles, 1902.
The organism is pear-shaped and bilaterally symmetrical. It is from 10 µ to 21 µ long and 5 µ to 12 µ broad and possesses a thin cuticle. Anteriorly an oblique depression is present, which functions as a sucking disc (fig. [19], s). Its edges are raised above the general surface and are contractile. It corresponds to a peristome and acts as an adhesive organ (fig. [20], b, c). No true cytostome is present. A double longitudinal ridge, representing axostyles, extends from the sucking disc to the tapering posterior extremity, which is prolonged as two flagella from 9 µ to 14 µ long.
Lamblia intestinalis possesses eight flagella (fig. 19). The first pair of flagella, which cross one another, arise in a groove formed by the anterior edge of the sucking disc. Two pairs of flagella (lateral and median) are inserted on the posterior edge of the disc, while the posterior flagella occur at the tapering posterior extremity of the body. Basal granules are found at the bases of the flagella. The median flagella are most active in movement, the anterior and lateral flagella being less motile, as they are partially united to the body for part of their length.
The nuclear apparatus is situated in the thin, anterior, hollowed part of the body. It is at first dumb-bell shaped, the “handle” of the dumb-bell being formed by a very slight connecting strand, which eventually separates, so that the flagellate becomes binucleate, and thus completes the general bisymmetry of the organism.
There is a karyosome in each nucleus. Other bodies of unknown function, and possibly composed of chromatin, occur on or near the axostyles.
Fig. 19.—Lamblia intestinalis. A, ventral view; B, side view; N, one of the two nuclei; ax., axostyles; fl1, fl2, fl3, fl4, the four pairs of flagella; s, sucker-like depressed area on the ventral surface; x, bodies of unknown function. (After Wenyon.)
Division has not been observed in the flagellate stages of the Lamblia, but it occurs within the cysts. The resistant cysts (fig. [20], e) are oval and are surrounded by a fairly thick, hyaline cyst wall. They measure 10 µ to 15 µ by 7 µ to 9 µ, and may be tetranucleate. According to Schaudinn, the cysts arise from the conjugation of two individuals, and nuclear rearrangement occurs.