176 



FUNCTIONS OF THE BRAIN. 



Experiment I — A. 



August 16. Sectioned anterior end of left crus. (Fig. 113, A.I.) Before the operation, 

 it was found that if the crab came to rest on its back, and the margin of the abdomen was gently 

 touched with the fingers, the legs on the opposite side would always be raised a fraction of a second 

 before the legs of the same side. When the movements are once started, they become general. 



After the operation, the left cheiicera is very restless, snapping and moving aimlessly 

 back and forth. The second left leg is also restless, and usually elevated higher than the others. 



I. Thoracic Reflexes. — Fifteen minutes later. 



a. Hand, placed on left side of thorax, causes a slight start of left legs and left gills. 

 Reverse experiment gives corresponding results. 



Figs. 112-113. — Brains of adult Limuli, that have been cut in various ways in order to determine the func- 

 tion of the principal brain regions and the course of the nerve impulses. All the figures show the brains from 

 the neural surface, with the right side toward the reader's right hand. The roman numerals indicate different 

 operations performed at different times on the same brain. 



b. A little later the results are somewhat varied. The right legs are less readily induced 

 to make reflex movements by stimulation of either side than are the left. 



c. Hand placed on the left side of thorax caused a slight stirring of the legs of both sides, 

 or a raising of the right or left legs, but no purposeful movements on either side. But placing 

 the hand on the right margin causes well marked, thrusting away movements of the right legs. 



d. Twenty-four hours later, repeated c. with same results. 



II. Abdomino-thoracic Reflexes. — a. Fifteen minutes after the operation. Hand placed 

 on left margin of the abdomen causes sudden depression of the gills of both sides and raising of 

 the right legs. Reverse experiment gives corresponding results. 



The gills on the side stimulated contract a little before those of the opposite side. This 

 is in marked contrast with the fact that the thoracic appendages of the opposite side always move 

 first when one side of tne abdomen is stimulated, showing that the abdominal reflexes 

 are mainly uncrossed, and the abdomino-thoracic are mainly crossed. 



