248 University of California Publications in Zoology [Vol. 11 



anterior sucker and the segments of the body closely contiguous 

 to it removed, there is a reason for the lack of responsiveness 

 in this regard. 



The anterior end relieved of the posterior portion of the body 

 will feed if given the opportunity, performs random movements 

 rather in excess of the normal individual, and if consisting of 

 half or more of the body length swims readily through the water. 

 The looping response is performed, rather clumsily, since the 

 animal is without the posterior sucker. 



Frequently groups consisting of several decapitated Dinas 

 are to be found in various places in the aquarium. To this 

 extent the thigmotaxis of the leech is expressed. I have kept 

 stones in the dish with such specimens for several weeks, but for 

 some reason the leeches do not accumulate underneath these 

 hiding places. Not so with the anterior ends, however, for these 

 soon find the stones, and remain persistently underneath them 

 until disturbed. 



Undulatory movements of respiration are made liy the various 

 portions of the body, but not to any considerable degree. The 

 posterior regions of the body, minus the anterior, are rather the 

 more proficient in the performance of these movements than any 

 other parts, though I have seen a small portion of the body with- 

 out either anterior or posterior sucker undulating itself rather 

 rapidly so as to secure more efficient aeration. 



5. Function of the Brain 



The function of the brain is, to a certain extent at least, the 

 production of spontaneity of movement. This is indicated by 

 the fact that there is a greater exce.ss of movements of this char- 

 acter in the anterior ends removed from the body than in the 

 decapitated specimens. This is markedly true even in leeches 

 some months after operation. To a certain degree, the brain is 

 a co-ordinating center, serving to make the locomotor responses 

 more efficient as the result of the proper interaction of the parts 

 producing the progressive movements. 



Bohn (1907) has claimed for Branchellion the power of 

 simple "phenomenes associatifs." Yerkes (1912) has found what 



