. Behavior of the lower organisms. Animal behavior; Invertebrates. turning toward the right side (Fig. 77). Spirostomum amhiguum and Spirostomum tenue swim backward and turn toward the aboral side. Opalina ranarum turns toward the more convex (right) side, Nycto- therus toward the aboral side (Fig. 78). Many of these or- ganisms show an additional reaction to strong stimuli, con- sisting in a marked contraction of the body. This is particu- larly noticeable in Spirostomum and Stentor. Many of the Ciliata do not as a rule swim freely through the water, but creep along sur- faces, keeping one si
. Behavior of the lower organisms. Animal behavior; Invertebrates. turning toward the right side (Fig. 77). Spirostomum amhiguum and Spirostomum tenue swim backward and turn toward the aboral side. Opalina ranarum turns toward the more convex (right) side, Nycto- therus toward the aboral side (Fig. 78). Many of these or- ganisms show an additional reaction to strong stimuli, con- sisting in a marked contraction of the body. This is particu- larly noticeable in Spirostomum and Stentor. Many of the Ciliata do not as a rule swim freely through the water, but creep along sur- faces, keeping one side against Fig. 77. —Reaction of Bursaria, ventral view, the Surface. This is true at i-5, successive positions occupied. tjmes Qf mQst Qf tJle organisms mentioned in the foregoing paragraph. It is much more usual in cer- tain other ciliates, belonging to the group of Hypotricha (Fig. 31, /; Fig. 81). In these animals the cilia of one side of the body are spe- cially modified for creeping, while the opposite side bears either few and weak cilia or none at all. The Hypotricha are usually found running about on the bottom, or on the surface of objects in the water. In addition to their creeping movements, they pro- duce by means of strong peristomal cilia a vortex leading back to the mouth. These animals of course do not revolve on the long axis as they progress, and the corresponding feature is likewise lacking in the reactions to stimuli. On coming in contact with an obstacle, or when otherwise stimulated, they stop or , FlG- j}-~ N-vct°- 7 1 therus. 1 he arrow to move backward a distance, then turn toward a cer- the right shows the tain structurally marked side, keeping in contact with direction of turning in J ' 1 ° . response to stimula- the substratum and not revolving on the long axis, tion, while the three This renders it much easier to observe the precise interjor arrows indicate 1 the direction of beat of method of reacting than in Paramecium, where the the cilia. A
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