. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PTEROPODA. 175 either the tentacle (fig. 110. 10 and 11,*), or the orifice (fig. 110. 12, /), through which it is protruded : the two flat surfaces are separated from each other when the cowls are closed by a longitudinal fissure (p), the margins of which form two prominent lips (o o). The lateral tentacles (£) are cylindrical, smooth, and terminated by rounded extremi- ties. They are hollow, and in their interior, three longitudinal bands of muscle and a nerve of considerable size are distinguishable, so that they can b
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PTEROPODA. 175 either the tentacle (fig. 110. 10 and 11,*), or the orifice (fig. 110. 12, /), through which it is protruded : the two flat surfaces are separated from each other when the cowls are closed by a longitudinal fissure (p), the margins of which form two prominent lips (o o). The lateral tentacles (£) are cylindrical, smooth, and terminated by rounded extremi- ties. They are hollow, and in their interior, three longitudinal bands of muscle and a nerve of considerable size are distinguishable, so that they can be retracted in the same manner as the horns of a snail, nothing re- maining externally to indicate their position, except the hole through which they are pro- truded. When thus inverted the tentacles are found lodged in the cavity of the head, with their apices directed inwards. The two smaller spheres of the hood or cowl are separated from each other by the longitudinal fissure (fig. 110. 11), which Fabri- cius, very inappropriately, called the mouth, although, at the same time, he was acquainted with the real mouth, and recognised it as such. This vertical fissure occupies the entire top of the head, and is continued for some distance both on its upper and under surface, or, more properly speaking, the real head is buried deeply in the interspace be- tween the two cowls, and when these are sepa- rated from each other, the following parts are seen situated between them : in the centre of the floor of the fissure is the vertical opening of the mouth (fig. 110. 13, u), between which and the borders of the hood (q], are the cres- centic spaces (•/•}, in which are situated the conical appendages to the head already men- tioned, and which are represented protruding from between the margins of the hood in fig. 110. 10 (*•). Conical Appendages to the Head. — The co- nical appendages to the head (Kopfkegel, Eschricht), when fully expanded, form a kind of star round the mouth
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