. Elements of comparative anatomy. Anatomy, Comparative. APPENDAGES OF VERMES. 133 .,> •world on the organism. They are especially developed in the Chosto- poda, the cephalic region of which is provided with contractile pro- cesses, either at the sides or in the middle line (Fig. 55, t t'). These processes are simple, or are further differentiated by segmentation, or even distinguished by the possession of secondary processes. By adaptation to the most varied conditions of life they are converted into very various structures, and serve for all kinds of functions. In the tubicolous Chastopod
. Elements of comparative anatomy. Anatomy, Comparative. APPENDAGES OF VERMES. 133 .,> •world on the organism. They are especially developed in the Chosto- poda, the cephalic region of which is provided with contractile pro- cesses, either at the sides or in the middle line (Fig. 55, t t'). These processes are simple, or are further differentiated by segmentation, or even distinguished by the possession of secondary processes. By adaptation to the most varied conditions of life they are converted into very various structures, and serve for all kinds of functions. In the tubicolous Chastopoda, where the cephalic region is that por- tion of the body which comes into closest relation with the surround- ing medium, the tentacles are converted into an important apparatus. They form tufts of contractile filaments on the cephalic lobes, where they are arranged in one or more rows (Terebella [cf. infra, Fig. 79, {], Hermella); or they may be con- verted into strong plume-like struc- tures (branchial tentacles) by the development of an internal support (cartilage), and. be beset with secon- dary branches; these, in addition to their respira- tory function, may also aid in the movement of the whole apparatus when seizing food (Serpulaceas). In some, these bran- chial tentacles are arranged in two groups, and resemble an open fan. In Siphonos- toma they form short simple filaments, with two longer delicate feelers. In others the base of the two halves of the tuft, which are separated on the dorsal line, is drawn out into a spirally-coiled ridge, on which the separate filaments are arranged (Sabellidas). When optic organs are formed on the separate filaments of the branchial tufts, the tentacles acquire new and important relations (Branchiomma). Some of the branchial filaments undergo other kinds of changes. In some Sabellida3 one or two of the primitively similar branchial tentacles (Protula) lose their respiratory function ; in others they are converted into club-shaped
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
