The animal kingdom : arranged after its organization, forming a natural history of animals, and an introduction to comparative anatomy . ry oflife, the respiratory wheels, and circulatory pumps, are hard at work in its inmost recesses. All these activeoperations belong, however, to the vegetative life, and do not indicate any consciousness or voluntary exertion onthe part of these beings. The currents of water are produced, as already mentioned, by the agency of the ciliaclothing the internal membranous surfaces ; and this action we have every reason to believe to be quite inde-pendent of the
The animal kingdom : arranged after its organization, forming a natural history of animals, and an introduction to comparative anatomy . ry oflife, the respiratory wheels, and circulatory pumps, are hard at work in its inmost recesses. All these activeoperations belong, however, to the vegetative life, and do not indicate any consciousness or voluntary exertion onthe part of these beings. The currents of water are produced, as already mentioned, by the agency of the ciliaclothing the internal membranous surfaces ; and this action we have every reason to believe to be quite inde-pendent of the animals will, and even beyond its control. It is a curious fact that Sulpa: are sometimes foundmaking their way through the water, after they have been deprived of their visceral mass by birds or entire nervous system is here reduced to a single ganglionic centre (Fig. 8, c), which is situated between thetwo orifices, sends filaments to each of them, and also distributes its branches over the general surface of themantle. No organs of special sensation are perceptible, and the only indication of common sensibility shown. 672 MOLLUSCA. by these animals, is the contraction of the mantle when the surface is touched, or when some irritatingparticle is drawn into the branchial orifice ; by this contraction n jet of water is spurted out, sometimes^a to a considerable distance. No beings possessed of a complex internal structure, adistinct stomach and alimentary tube, a pulsating heart, and ramifying vascularapparatus, with branchial appendages for aerating the blood, and highly-developedsecretory and reproductive organs, can be imagined to spend the period of their ex-istence in a manner more completely vegetative than these. All the Tunicata above described appear to participate in a very remarkable peculi-arity in the function of circulation. The heart is very simple in its structure, beingmerely a contractile dilatatiun of the principal trunk, without any distinct divis
Size: 1210px × 2065px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorwe, bookcentury1800, bookdecade1840, booksubjectanimals
