ACQUIRED DIFFERENCES. 11 



involved the use of the shield in one hand and spear or 

 sword in the other, he found by experience that wounds 

 on the left thorax, where the heart lies, were more fatal 

 than those on the right, consequently he learnt to hold 

 his shield on the left side and this led to a more active 

 use of the right arm and hand in the wielding of offensive 

 weapons. The condition thus established we may parallel 

 with that of the Mollusc or the hermit crab; Pagurus 

 carries his shield or shell on one side and fights with his 

 hypertrophied limb on the other side. I confess this last 

 view seems to me preferable to those which seek an 

 explanation in extra blood flow, in uterine position, or 

 in visceral weight. Either by the preferred use of 

 weapons in the right hand, or by some other determining 

 cause, man certainly at an early period selected Liis dexter 

 hand, and when later he began to draw, to sculpture stone 

 or wood, or to inscribe word- symbols he continued to use 

 his right hand and thus fixed the memory of objects or 

 symbols in that part of his left hemisphere whence 

 proceeded the motor impulses. 



But before he began to write he had been able to speak 

 and to understand speech ; why did the physical sub- 

 stratum of incoming and outgoing speech processes fix 

 itself in the left hemisphere? It is hard to say, unless 

 we suppose that already righthandedness had established 

 a pre-eminent functional activity in the left brain. 



Now we come to the final point : Is the pre-eminent 

 functional activity of the left brain, which in one way 

 or other has been established in the human race, still 

 continuing to be beneficial to man, or is it the contrary ? 

 The question, to my mind, is one of much difficulty and 

 seriousness. In the case of every other paired organ the 

 functions of right and left seem to be identical, as we see 

 in the lungs, kidneys, sexual structures, sense organs or 



