The simplest forms are thread-like bodies, flat or round, 3 mm. long and 0·3 mm. in diameter, but they may be 12 mm. long by 2·5 mm. broad. The narrow end is the head, which in life invaginates and evaginates, but there is no indication of any suckers, except an inconstant terminal depression. In addition to these simple forms the most complicated and irregular forms occur, due to the formation of buds (heads) at various parts. The detachment and growth of a head account for the presence of more than one worm in a cyst. The irregularity in form is also increased by the presence in the subcuticular tissue of the worm of reserve food bodies. These bodies are supposed to be of this nature and are spherical, 100 µ to 300 µ in diameter, but also much elongated.
Calcareous bodies in the Japanese worms were 7·5 µ to 12 µ; in the Florida worms 8·8 µ to 17·6 µ.
Fig. 217.—Dipylidium caninum: on the left, the scolex, neck and the first proglottids; on the right, at the top, a packet of ova; below, hooks of the rostellum, side and front views; below, an ovum. Various magnifications. (After Diamare.)
Fig. 218.—Dipylidium caninum; egg showing a, egg-shell (vitelline membrane of Moniez); b, albuminous coat; c, internal shell formed of or secreted by an outer layer of blastomeres (Moniez); d, hexacanth embryo. (After Benham and Moniez.)
Mode of Infection.—Probably from eating uncooked fish.
Distribution.—Japan, Florida.