A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . the moUusca; it isexercised by the skin, which iseverywhere soft and lubricous,and in a higher degree by the „ . ^ ,, 1 • 1 /r. T n^ Iig- 1-2- Lenton Squamosum.^ fringes of the bivalves (fig. 12), ° and by the filaments and tentacles {vihraculd) of the gasteropods ;the eye-pedicels of the snail are evidently endowed vrith gTcatsensitiveness in this respect. That shell-fish are not very sensi-ble of pain, we may well believe, on account of their tenacity oflife, and the extent to which they have the power of repr
A manual of the Mollusca, or, A rudimentary treatise of recent and fossil shells . the moUusca; it isexercised by the skin, which iseverywhere soft and lubricous,and in a higher degree by the „ . ^ ,, 1 • 1 /r. T n^ Iig- 1-2- Lenton Squamosum.^ fringes of the bivalves (fig. 12), ° and by the filaments and tentacles {vihraculd) of the gasteropods ;the eye-pedicels of the snail are evidently endowed vrith gTcatsensitiveness in this respect. That shell-fish are not very sensi-ble of pain, we may well believe, on account of their tenacity oflife, and the extent to which they have the power of reproducinglost parts. Muscular System. The muscles of the moVusca are prin-cipally connected with the skin, which is exceedingly contractilein every part. The snail affords a remarkable, though familiar * ]\Ir. Owen regards the membraneous lamella between the oral tentaclesand in front of the mouth, as the seat of the olfactory sen!?e. See Fuj. 44. t Iig. 12. Lepton sqaumosmn Mont.,^ from a drawing by Mr. ^UJer, inthe British Mollusca; copied by permission of Mr. Van STRUCTURE AND PHYSIOLOGY OF THE MOLLUSCA. 25 instance, when it draws in its eye-stalks, by a process like theinversion of a giove-finger; the branching gills of some of thesea-slugs, and the tentacles of the cuttle-fishes, are also emi-nently contractile.* The inner tunic of the ascidlans (fig. 8, t.) presents a beau-tiful example of muscular tissue, the crossing fibres having muchthe appearance of basket-work; in the transparent salpians,these fibres are grouped in flat bands, and arranged in charac-teristic patterns. In this class {tunicata) they act only assphincters (or circular muscles), and by their sudden contractionexpel the water from the branchial cavity. The muscular foot ofthe bivalves is extremely flexible, having layers of circular fibresfor its protrusion, (fig. ) and longitudinal bands for its re-traction (fig. 30 h); its structure and mobility has been com-pared to that of the human
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectmollusks, bookyear185
