30 cm. in length by 1·4 mm. in breadth, and is composed of 500 to 600 proglottides. The scolex is provided with four large round suckers and a retractile rostellum surrounded by five concentric rings of hooklets, about 110 in all, 18 μ long. The rostellum when invaginated forms a kind of pouch which gives it the appearance of an apical sucker. In a recent communication Blanchard states that not only is the rostellum armed, but the suckers also are provided with hooklets. The neck is very wide, thick, depressed antero-posteriorly and furrowed laterally. The proximal segments are broader than long, the distal longer than broad (2 by 1·4 mm.). The last 100 proglottides are gravid and form one-half the length of the entire strobila. They resemble apple-seeds in shape. The genital pores are unilateral and open near the proximal corner of each segment. The cirrus pouch is fusiform, the ductus ejaculatorius very long and sinuous, the testicles over 50 in number. The receptaculum seminis is unusually long and broad; it extends to the middle of the segment and communicates with the oviduct. The uterus is composed of a number of tubes rolled up on each side into an almost spherical coil. When filled with ova the windings of the uterus unroll and extend throughout the proglottis; they then lose their walls, so that the eggs come to lie free in the parenchyma. The eggs then become surrounded, singly or in small groups, by parenchymatous cells forming egg-balls, of which from 300 to 400 may be present in each segment. The globular onchosphere (8 μ to 15 μ) is surrounded by two perfectly transparent shells, the outer one bearing two pointed projections.
Fig. 203.—Davainea asiatica, sagittal section of gravid segment. (After Linstow.)
The cystic stage is unknown. Blanchard suggests that it might be found in cockroaches (Periplaneta orientalis, P. americana, etc.). He points out that the parasite has a wide distribution within the tropics, and that cases of infection have occurred in islands, in seaports, and on board ship. The cockroach is cosmopolitan in distribution, it infests ships and contaminates food. Other tapeworms of the genus Davainea are known to spend their larval stage in insects and molluscs. According to Grassi and Revelli, some of these tapeworms—as, for instance, D. proglottina of fowls—may dispense with an intermediary invertebrate host and spend both their larval and adult stages within the body of the same host.
Pathogenesis.—We know nothing of the pathogenesis of this form of tæniasis. The parasite has been found almost exclusively in young children.
