. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage. Zoogeography -- Geographical distribution; Animal ecology. THE PELAGIAL 229 ambulaeral feet, which make a free-swimming life possible until their increase in weight outruns their enlargement of surface. In general this increase of surface by projections is not widespread; it appears only among small and very small animals. The great majority of pelagic animals get on without this means of suspension. Water resistance, actively secured by means of swimming, is the most widespread
. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage. Zoogeography -- Geographical distribution; Animal ecology. THE PELAGIAL 229 ambulaeral feet, which make a free-swimming life possible until their increase in weight outruns their enlargement of surface. In general this increase of surface by projections is not widespread; it appears only among small and very small animals. The great majority of pelagic animals get on without this means of suspension. Water resistance, actively secured by means of swimming, is the most widespread means of preventing sinking. Such motion may consist largely of force exerted opposite the direction of gravitational pull as in the pteropods, or may be a small component of lateral motion as in the sharks. The effectiveness of the reaction is measured by the size of the body and its rapidity of motion. The water resistance of a body is proportional to its projection on a plane at right angles â U '' Fig. 54.âJuvenile sea urchin (Arbacia pustulosa): /, ambulacra! feet; p, pedicel- laria; St, spines. After Korschelt and Heider. to the line of motion, and to the square of the speed with which the body moves. Cilia and lashing hairs, on account of their small surface, are not very effective and are found mainly among protozoans, among very small Metazoa, and among these especially in larval stages. Great numbers of cilia are required to support even small animals. In the almost microscopically small larvae of echinoderms, Balanoglossus, worms, etc., they are arranged in narrow rings or bands. When the larvae increase in size, further support can be gained only by rela- tively great increase in the length of the bands of cilia. The larvae of echinoderms rarely reach any considerable size during their free- swimming stage; but in those which do, the bipinnarians and auricu- larians, reaching a length of about 5 mm., the ciliary bands are folded and bent in a remarkable way
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
