Family. Dipylidiidæ, Lühe, 1910.
Genus. Dipylidium, R. Lkt., 1863.
Rostellum retractile, with several rings of alternating hooks; the latter with a disc-like base, having the shape of the thorns of a rose. Genital pores opposite; genitalia double. Testes very numerous in the central field; ovary with two lobes; the vitellaria, which are smaller, behind them; the uterus forms a reticulum, in the network of which the testicular vesicles lie; later on it breaks up into sacs enclosing one or several eggs. The eggs have a double shell.
Dipylidium caninum, L., 1758.
Syn.: Tænia canina, L., 1758, p. p.; Tænia moniliformis, Pallas, 1781; Tænia cucumerina, Bloch, 1782; Tænia elliptica, Batsch, 1786; Dipylidium cucumerinum, Lkt., 1863.
This worm measures 15 to 35 cm. in length and 1·5 to 3 mm. in breadth. The scolex is small, rhomboidal, and has a club-shaped rostellum on which there are, in three to four rings, forty-eight to sixty hooks resembling rose thorns, the size of those in the foremost being 11 µ to 15 µ and those in the hindmost ring 6 µ. The neck is very short, the most anterior segments broad and short, the middle as long as they are broad; the mature segments are longer than wide (6 to 7 mm. by 2 to 3 mm.), fairly thick, are frequently of a reddish colour, and when cast off resemble cucumber seeds. The genital pores lie symmetrically at the lateral margins; the roundish egg sacs, arising from the uterine reticulum, contain eight to fifteen eggs embedded in a reddish cement substance (in life). The eggs are globular (43 µ to 50 µ,); the embryonal shell (embryophore) is thin, the oncosphere measures 32 µ to 36 µ. Surrounding the embryophore is an albuminous coating, and outside this the thin vitelline envelope (fig. 218).
Fig. 219.—Dipylidium caninum: central portion of a proglottis. C.p., cirrus sac; V.s., vitellaria; Ex.v., excretory vessels; T., testicles lying in the meshes of the uterine reticulum which laterally forms pouches; O., ovary; U., reticulum of uterus; V., vagina and seminal receptacle (below ovary). Magnified. (After Neumann and Railliet.)