. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. CESTODA. 327 the head armature is very weak, and consists of a lobed fringed expansion. The apex of the head often ends in a conical projection, the rostellum, which is armed with a double circle of hooks, while the lateral surfaces of the head are furnished with four suckers (Ttenia, fig. 263). In other cases only two suckers are present (Bothriocephalus); or we find suckers of more complicated structure and beset with hooks (Acomthoibothrium), or four protrusible probosces beset with recu
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. CESTODA. 327 the head armature is very weak, and consists of a lobed fringed expansion. The apex of the head often ends in a conical projection, the rostellum, which is armed with a double circle of hooks, while the lateral surfaces of the head are furnished with four suckers (Ttenia, fig. 263). In other cases only two suckers are present (Bothriocephalus); or we find suckers of more complicated structure and beset with hooks (Acomthoibothrium), or four protrusible probosces beset with recurved hooks (Tetrarhynchus); while in other genera the head armature presents various special forms. That portion of the animal which follows the and is dis- tinguished as the neck shows, as a rule, the first traces of com- mencing segmentation. The rings, which are at first faintly marked and very narrow, become more and more distinct and gradually larger the further they are removed from the head. At the pos- terior extremity the segments or pro- glottides are largest, and have the power of becoming detached. After separation they live independently for a long time, and sometimes even in the same medium. The simplicity of the internal or- ganization corresponds with the simple appearance of the external structure. Be'neath the delicate external cuticle is a matrix consisting of small cells, , , , •. , FIG. 263.—Head of Tcenia. soJium, viewed in which are scattered glandular ceils. from the front (apical surface), with Beneath the matrix there is a delicate rosteiium and double circle of hooks. The four suckers are visible. superficial layer of longitudinal mus- cular fibres, and next a parenchyma of connective tissue, in which strongly-developed bundles of longitudinal muscular fibres, as well as an inner layer of circular muscles, are embedded; both these muscular layers are traversed, principally at the sides of the body, by groups of dorso-ventral muscular fibr
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