secondary pores is present (Figs. 38 and 41, _for.sec_). Flame-cells occur at the end of the fine tubules (Fig. 38), and the whole system is well developed, but may undergo degenerative changes in the older proglottides. The central nervous system varies according to the degree of differentiation of the rostellum; and, owing to the difficulty of staining the nerves and the contradictory statements of authors, we do not yet possess a fully reliable account of the nervous system even of the commoner Taeniae. Free nerve endings and other sensory terminations have been recently stated to exist in the cuticle of Cestodes and Trematodes. If true, this would tend to show that the parasitic mode of life of these animals demands a complex nervous system comparable with that of the Turbellaria. [Illustration: FIG. 41.—Diagrammatic transverse section of _Schistocephalus solidus_ Crepl., from the Wild-duck, illustrative of the Cestodes with uterine aperture (_uto_). × 12. _cs_, Cirrus-sac; _for.sec_, one of the paired lateral openings of the excretory vessels; _ln_, longitudinal nerve; _ov_, ovary; _ovd_, oviduct; _par.m_, parenchymatous muscles; _r.sem_, receptaculum seminis; _sh.gl_, shell-gland; _te_, testes; _ut_, uterus; _uto_, uterine pore; _vag_, vagina; _vd_, vasa deferentia; _yd_, yolk-duct; _yg_, yolk-glands (black); ♂, male, ♀, female genital aperture. (After Riehm.)] The reproductive organs, unlike the preceding systems, are discontinuous from one proglottis to the next. The male and female organs and their mutual connexions, especially in the unsegmented Cestodes, may be compared in detail with those of Trematodes, but the difference between the arrangement of the generative organs of various Cestodes is very great.[107] The penis (Fig. 41, _cs_) is evaginated through the male pore (Fig. 41, ♂), and inserted far into the vagina (♀, _vag_) of the same or another segment of the tape-worm. {87}[Illustration: FIG. 42.—A, Free-swimming, six-hooked larva of _Bothriocephalus latus_ Brems. (the broad tape-worm of Man), still enclosed in a ciliated (possibly cellular) double membrane or mantle. In this condition it may continue to live in water for a week or more, but eventually throws off its ciliated coat (as in B) and commences to creep about vigorously by the aid of its hooks, in search of its first host, which is at present unknown. (After Schauinsland.) × 600.]