The Journal of experimental zoology . gative orientation isevidenced by animals of all ages. It is most perfectly ex-pressed when the chiton is completely submerged. The hori-zontal position assumed at the water level is a special conse-quence of stimuli associated with the water level. The tendency to upward creeping is clearly evident upon 208 LESLIE B. AREY AND W. J. CROZIER surfaces inclined at any angle above 30° with the these tests the larger animals are best. Observations in the field and many tests in the laboratoryshow clearly that there is no tendency for Chiton to pr
The Journal of experimental zoology . gative orientation isevidenced by animals of all ages. It is most perfectly ex-pressed when the chiton is completely submerged. The hori-zontal position assumed at the water level is a special conse-quence of stimuli associated with the water level. The tendency to upward creeping is clearly evident upon 208 LESLIE B. AREY AND W. J. CROZIER surfaces inclined at any angle above 30° with the these tests the larger animals are best. Observations in the field and many tests in the laboratoryshow clearly that there is no tendency for Chiton to preserve aconstant dorsoventral orientation. In rock crevices they occurupside down with great frequency. Careful observation of the movements of a chiton during geo-tropic orientation affords a clue as to the nature of the determin-ing stimulus. Accurate outlines of a specimen orienting in thisway are given in figure 12. Inspection of these outlines willshow that the sequence of events in orientation is as follows: riinz). C5l>^DLEL PRESSED To SLASs) Fig. 12 Outlines of the successive positions assumed by a Chiton in ori-enting upward from a horizontal position, under water, on a vertical surface;ventral aspect. (Traced through glass, on thin paper.) X f. The girdle becomes freed from the substratum, so that the ani-mal remains attached by the foot only; when in the horizontalposition (fig. 12, II), the weight of the body causes it to fallslightly, producing an uneven tension in the muscles, those onthe higher side being stretched. The animal swings until thisunilateral tension is relieved. It turns anterior end up, probablybecause that end is the more sensitive. The tendency is for theanimal to turn toward the stretched side; the tenser muscles arethe ones which contract. With animals in the vertical position(fig. 12, V) the downward pull of the creatures weight is exertedat the posterior end. THE SENSORY RESPONSES OF CHITON 209 The chief ethological importance
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1919
