. Cassell's natural history. Animals; Animal behavior. well-developed foot organs, which lead a I'oaming life, tlie exceptions being very few, and which are carnivorous and predaceous—thej' are the Errantia : secondly, those which live in protecting tubular structures, and wliich have feebly developed feet, and are called the Tubicola. In examining these many-bi-istled Worms it is advisable to employ certain descriptive terms. Thus, the first segment of the body is called the prostomiura, and the mouth opens on it: the second is tlie peristomitnn. When the three front segments are united, or w
. Cassell's natural history. Animals; Animal behavior. well-developed foot organs, which lead a I'oaming life, tlie exceptions being very few, and which are carnivorous and predaceous—thej' are the Errantia : secondly, those which live in protecting tubular structures, and wliich have feebly developed feet, and are called the Tubicola. In examining these many-bi-istled Worms it is advisable to employ certain descriptive terms. Thus, the first segment of the body is called the prostomiura, and the mouth opens on it: the second is tlie peristomitnn. When the three front segments are united, or when they differ from those which come after, they are called the head or cephalic segments ; but when this is not the case the Worm is said to be acephalous. The head has various appendages according to the genei-a. An- tennse are soft filaments varying in number from one to five, and they arise directly from the head, are not retractile, and are usually jointed at the base. Sometimes palpi exist, and they are soft, entire, or jointed processes, arising from the sides of the mouth. The tentacles are soft, bristly, or thread-shaped, non-retractile processes, which arise from each side of the segments of the head in pairs, and spread laterally. They are often very long, and are contractile in the acephalous genera. The month is underneath the head, and is a ; B,nimub, 4.'.; a, ciirj: 6, rouud or Opening to the gullet. It has usually a plain margin. In the acephalous genera it is terminal, and has external tentacles, but there are no jaws, and in the cephalous it is nearly terminal and looks forward horizontally. It is almost always furnished with a proboscis in the cephalous tribes; that is to say, the oesophagus or gullet can be protruded. It consists of two seg- ments, and can be put forth at pleasure by a process of turning inside out. It is often armed with horny Jaws, in opposite pairs, or is roughened on the surface wit
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Keywords: ., bookcentury1800, bookdecade1890, booksubjecta, booksubjectanimals
