CHAPTER XL 

 FUNCTIONS OF THE BRAIN. 



PART I. 



Introduction. In the preceding chapters, we have shown that there is a 

 far reaching resemblance in structure and development between the brains of 

 vertebrates and arachnids. In this chapter, we shall show that they agree in 

 function, and in their physiological relations to other parts of the body. 



In the arachnids, the location of several important cerebral centers is already 

 clearly indicated by the peripheral termination of the associated nerves, as for 

 example, the visual, gustatory, cardiac, and respiratory centers. Nevertheless, 

 it seemed highly desirable, indeed imperative, that there should be some experi- 

 mental evidence to demonstrate the course of the principal nerve impulses, and to 

 locate by experiment the centers that control a group of similar activities, or that 

 bring them into coordinate relation with other activities. 



Although Limulus has the largest forebrain, or hemispheres, of any inverte- 

 brate known, it does not approach such animals as the hymenoptera, the cephalo- 

 pods, the crayfish, or the lobsters, in alertness, or in the variety of its responses to 

 visual, tactile, or other stimuli. When compared with the members of its own 

 class, such as the spiders and scorpions, it appears stupid and quite unaffected 

 by the events going on in the world about it. Limulus, no doubt, appears to lead 

 a sluggish life in the muddy bottoms of deep waters; but we should be greatly in 

 error if we were to estimate the probable volume and complexity of its coordinating 

 centers, or of what corresponds to the hemispheres of vertebrates, by its so-called 

 ' 'manif estation of intelligence. ' ' Indeed Limulus would furnish very little material 

 that could be used for experimentation or observation along these lines. But, 

 for the study of some of the simpler reflexes, Limulus is not excelled by any other 

 animal. 



The following experiments were made in the summer of 1897, at Woods Hole. 

 In the summer of 1898, Mr. Raymond Pearl, then a student at Dartmouth, work- 

 ing under my direction, repeated many of my experiments, and the following year 

 added others of his own. More than seventy different operations were performed, 

 mostly on adult animals. They generally involved the transecting, or the remov- 

 ing, of various parts of the brain, or cord, in order to determine the path of nerve 

 impulses, or to locate the centers of control. 



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