Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 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 rostelluni, which is armed with a double circle of hooks, while the lateral surfaces of the head are furnished with four suckers (Tn'iiia, fig. 263). In other cases only two suckers are present (Bothriocephalus) ; or we find suckers of more complicated structure and beset with hooks (Acanthobot/trium), or four protrusible probosces beset wit
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 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 rostelluni, which is armed with a double circle of hooks, while the lateral surfaces of the head are furnished with four suckers (Tn'iiia, fig. 263). In other cases only two suckers are present (Bothriocephalus) ; or we find suckers of more complicated structure and beset with hooks (Acanthobot/trium), or four protrusible probosces beset with recurved hooks (Tetrarhyncus); while in other genera the head armature presents various special forms. That portion of the animal which follows the head 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. Beneath the delicate external cuticle is a matrix consisting of small cells, in which are scattered glandular cells. Beneath the matrix there is a delicate 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 clorso-ventral muscular fibres. The power which the proglottis possesses of altering its form is due to the interaction of all these muscles. By means of them it is able to shorten itself
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