The laws and mechanics of circulation, with the principle involved in animal movement . —Fundamentally, the body of the worms is a hol-low cylinder, composed of circular and longitudinal muscularlayers, the former external, the latter internal. In Annelides,the longitudinal fibres are increased, forming two dorsal andtwo ventral layers, leaving a lateral groove. In addition tothis, a layer of transverse fibres, generally in the form of dis-tinct bundles, passes from the ventral median line to the lateralgrooves, which enables the animal to flatten its body whenswimming, passing through the wat
The laws and mechanics of circulation, with the principle involved in animal movement . —Fundamentally, the body of the worms is a hol-low cylinder, composed of circular and longitudinal muscularlayers, the former external, the latter internal. In Annelides,the longitudinal fibres are increased, forming two dorsal andtwo ventral layers, leaving a lateral groove. In addition tothis, a layer of transverse fibres, generally in the form of dis-tinct bundles, passes from the ventral median line to the lateralgrooves, which enables the animal to flatten its body whenswimming, passing through the water by graceful undulationsof the body, which is flattened out, ribbon-like. The suckersare special differentiations of the dermo-muscular tube, which 466 DUALISM DKMONSTRATKD. agree with one another in all the essential points of theirstructure. The great relative thickness of the muscular cylinder is seenin the following illustration (Fig. 13, A, B, in). During feeding and locomotion the muscular layers are af-fected differently, the one directly the opposite of the other, B B J).
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