. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 372 prscoral or cephalic) lobe are widely distributed. Eye-spots may also be pi-esent upon the posterior end of the body [Fahricia), or may be regularly repeated upon the sides of each segment {Poli/o])hthaImus). In species of Sabella, pigment-spots with refractive bodies are found even upon the branchial filaments. The large cephalic eyes of the genus Alciope* are the most highly developed, being provided with a large lens and a complicated retina. The presence of auditory organs seems
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 372 prscoral or cephalic) lobe are widely distributed. Eye-spots may also be pi-esent upon the posterior end of the body [Fahricia), or may be regularly repeated upon the sides of each segment {Poli/o])hthaImus). In species of Sabella, pigment-spots with refractive bodies are found even upon the branchial filaments. The large cephalic eyes of the genus Alciope* are the most highly developed, being provided with a large lens and a complicated retina. The presence of auditory organs seems less frequent. They appear as paired otolithic vesicles upon the oesophageal ring of Arenicola, Fahricia, some Sahellidce and young Terebellidce; etc. Besides the tentacles, cirri and elytra, other portions of the surface of the body may be sensi- tive to tactile sensations. On such parts there are either stiff hau-s and tactile setse, or, as in Sphcerodorum, special tactile warts with nerve terminations. Reproduction.—In the smaller Chcptopoda asexual genei'ation by fission and gemmation may occur. Either (fissiparous reproduction) a large number of segments of the parent be- come separate and give rise to the body of the new worm, as for example in Syllis prolifera, where a series of the posterior segments, which are filled -with ova,, become separated by a simple transverse fission, after the formation of a head provided with eyes; or (gemmiparous repro- duction) a single segment only, usually the last, becomes the starting-point for the formation of a new indi\ddual. In this way Autolytus pro- lifer, one of the Syllida:, asexually reproduces itself, giving rise to a male and female sexual form, known respectively as Pohjbostrichiis Miillerif (male) and Sacconereis helgolandica (female). This is a case of alternation of gene- rations, for the asexual form, Autolytus, gives rise by budding in the long axis to the sexual forms (fig. 302). In this case a whole series of segme
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
