Fig. 231.—Hymenolepis diminuta: cysticercoid from the rat flea (Ceratophyllus fasciatus). a, remains of primary vesicle; b, fibrous layer; c, radially striated layer resembling cuticle; d, layer of columnar cells; e, parenchymatous layer of irregularly disposed cells; f, parenchymatous layer. (Stephens, after Nicoll and Minchin.)
Nicoll and Minchin[283] found in the body cavity of 4 per cent. of rat fleas (Ceratophyllus fasciatus) the cysticercoid of Hymenolepis diminuta. That it belonged to this species was shown by its unarmed rostellum and by feeding; 340 fleas were fed to white rats and fourteen worms obtained, i.e., about 4 per cent., thus corresponding to the infection of the fleas. The development in the flea probably begins in the pupal stage, the eggs being ingested by the older flea larvæ. The larva is 0·31 by 0·25 mm.; tail 0·8 mm., scolex 0·075 by 0·09 mm., suckers, 0·055 mm. in diameter. Microscopically it shows—(1) externally a radially striated layer resembling cuticle, (2) a layer of columnar cells, (3) parenchymatous layer continuous with the tail, (4) fibrous layer around the small caudal vesicle, then the parenchymatous scolex at the bottom of the secondary cavity.
Nicoll and Minchin (loc. cit.) found a cysticercoid[284] in the rat flea Ceratophyllus fasciatus which was probably that of Hymenolepis murina. Body 0·16 mm., tail 0·19 mm., scolex 0·096 mm. in diameter. Rostellum has twenty-three spines in a single row. Length 0·017 mm., handle 0·01 mm., guard 0·007 mm., prong 0·007 mm. Sucker 0·042 mm. Although this cycle, then, for H. murina also exists, it is not probable that rats (or man in the case of H. nana if this be considered distinct) infect themselves in this way, as they hardly ingest all the necessary fleas to account for the massive infection which frequently exists in rats (and man), so that Grassi’s cycle holds good as the predominant method. Xenopsylla cheopis has also been found by Johnston to harbour both cysticercoids in Australia.
Fig. 232.—Hymenolepis lanceolata. Natural size. (After Goeze.) To the right above, two hooks. 120/1. (After Krabbe.)
Hymenolepis lanceolata, Bloch, 1782.
Syn.: Tænia lanceolata, Bloch, 1782; Drepanidotænia lanceolata, Railliet, 1892.
The parasite measures 30 to 130 mm. in length and 5 to 18 mm. in breadth; the head is globular and very small; the rostellum is cylindrical, with a circlet composed of eight hooks (31 µ to 35 µ in length). The neck is very short. The short segments increase gradually and equally in breadth, but only a little in length; the female glands lie on the side opposite to that on which the genital pore is situated; the three elliptical testes are on the same side as the pores; the cirrus is armed and slender. The eggs have three envelopes and are oval (50 µ by 35 µ), the external envelope is thin, the middle intermediate layer or envelope is not so marked as in H. diminuta, and the internal one is very thin and sometimes has polar papillæ, as in Hymenolepis diminuta and H. nana.