. Carnegie Institution of Washington publication. 98 Papers from the Marine Biological Laboratory at Tortugas. DOES ONE RAY HAVE GREATER FUNCTIONAL VALUE IN LOCOMOTION THAN ANOTHER? The experiments of Preyer (1886-1887), m which he tested several species of starfish to see if one ray had greater functional value than another in locomotion, seem to answer the question in the negative except in the case of a specimen of Astropecten pentacanthus, which showed a decided tendency to use ray 4 (d of Jennings's paper and my own) as director. In general, however, Preyer concluded that one ray has no g
. Carnegie Institution of Washington publication. 98 Papers from the Marine Biological Laboratory at Tortugas. DOES ONE RAY HAVE GREATER FUNCTIONAL VALUE IN LOCOMOTION THAN ANOTHER? The experiments of Preyer (1886-1887), m which he tested several species of starfish to see if one ray had greater functional value than another in locomotion, seem to answer the question in the negative except in the case of a specimen of Astropecten pentacanthus, which showed a decided tendency to use ray 4 (d of Jennings's paper and my own) as director. In general, however, Preyer concluded that one ray has no greater functional value in locomotion than another (fig. i). While Jennings (1907) in his work on the starfish has not taken up this particular problem, he has made a rather extensive study in order to determine if Aster i as forreri de Loriol tends to right itself on any special pair of rays and he concludes that the rays lying close to the madreporic plate are more often used than any others. FIG. i.—Diagram of a starfish in the normal position, , r>^l,_ / o\ c~A with aboral surface uppermost. The labeling of the -DOml (.IQOOj Tina rays by numerals is that used by Preyer and Bohn; cn^r>im»-nc r>f A c/^W/rc the labeling of the rays by letters is that used by ASteTlOS Jennings, Cole, and the writer. The madreporic plate show " Une SOrte de preference is indicated by the black spot and is labeled m. pour certains bras," especially when the individuals are of a large size. The rays J (c) and 5 (e) of one individual were used most frequently as directors in locomotion. Bohn, however, does not draw the conclusion that A. rubens shows any very definite habit in this respect. Recently, in a preliminary report (1909), I stated that Echinaster crassispina does not show any tendency to use a special ray or pair of rays as a director. This conclusion was based on a considerable number of observations with directive light excluded, but the work was not a careful
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