EXPERIMENTS. 177 



b. Twenty-four hours later. The right legs frequently perform spontaneous movements, 

 as in a normal crab, but the left are quiet unless stimulated. 



c. Hand placed on the right margin of the abdomen causes very vigorous thrusting away move- 

 ments of left legs, more vigorous than can be produced in any other way. The right legs may 

 be raised and flexed in a sort of spasm, or may not; but they never thrash about as the left legs 

 do. The movements of the left legs are governed entirely by the stimulation, and cease when 

 the fingers are removed from the margin of the abdomen. 



d. When the hand is placed on the left margin of the abdomen the right legs immediately 

 move back and forth in the usual manner, the left legs either remaining quiet, or spasmodically 

 flexed. If the crossed reflexes of the right legs are violent they may not cease on removing 

 the stimulus, and the animal may attempt to regain its upright position. 



There is a marked difference between the movements of the right legs, in d, and of the left 

 ones in c. The movements of the right legs are those of a normal crab when stimulated. The 

 left legs may move more vigorously, in response to a crossed abdominal impulse, than the right, 

 but their movements are aimless, and cease with the cessation of the stimulus. 



These experiments show conclusively the controlling and directing effect of the cerebral 

 hemispheres. 



Experiment I — B. 



Same animal. Thirty-six hours later. Cut all the free, post-oral cross commissures of the 

 thorax, leaving the vagus commissures intact. (Fig. 113, A. II.) 



I. Thoracic Reflexes. — a. Ten minutes after the operation. Hand on either margin of 

 the thorax causes slight movements of the legs on the same side, but none whatever on the op- 

 posite one; except that when the right side was stimulated, the second leg on the left made vigor- 

 ous movements. 



These experiments were repeated at intervals of one or two hours, with the same results, 

 except that the uncrossed reflexes gradually became more pronounced. 



The experiment shows that there are crossed and uncrossed thoracic reflexes, and that the 

 crossed ones pass to the opposite side through the thoracic and the forebrain commissures. 



II. Abdoinino-thoracic Reflexes. — a. Fifteen minutes after the second operation, hand 

 placed on the margin of the abdomen produced only faint movements of the legs of the same side. 

 On repeating the experiment, at intervals of an hour, the crossed, abdomino-thoracic reflexes 

 gradually appeared, and three or four hours later became well marked. 



III. Gustatory Reflexes. — a. After cutting the left crus, the normal chewing movements 

 could be readily produced, except that the second left leg was spasmodic and irregular in its 

 movements. 



b. After cutting the cross commissures, the chewing movements that could be induced on 

 the right were very feeble; none at all could be induced on the left. These negative results were 

 probably due to the feeble condition of the animal. 



IV. Olfactory Reflexes. — On stimulating the olfactory organ with the electrodes, move- 

 ments of all the right thoracic appendages and the first two on the left are produced. 



Experiment II — A. 



August 6 Female. Sectioned thoracic cross commissures and the right crus back of 

 sixth leg. (Fig. 113, B, I.) 



August 14. Crab is very restless when taken from the water. The thoracic appendages 

 are in almost constant motion, waving about in an aimless manner. 



I. Thoracic Reflexes. — August 14. Uncrossed reflexes well marked; crossed, indistinct or 

 absent. 



