THE DOCTRINE OF HUMAN AUTOMATISM. 275 



but I now quite admit that there is much to be said in favour of 

 the second. For the denial of consciousness to insects, however, 

 I cannot see any other argument than that if " molecular motion " 

 be competent to do the work, sensation would be a useless sur- 

 plusage, — an application of the doctrine of final causes which can 

 scarcely be admitted as having any scientific validity. 



The study of the conditions of instinctive action having thus 

 landed us in the conclusion of its dependence upon a mechanism 

 of nerves and muscles excited to activity by external impressions, 

 we apply the same method of inquiry to the conditions of that 

 rational action with which we credit the higher vertebrates, and of 

 which we trace the dawnings among the lower. 



It is now universally acknowledged that the meaning of that 

 complex aggregate of ganglionic centres which makes up the 

 brain of man, can only be rightly understood by a careful study 

 (i) of the comparative structure of the brains of the lower verte- 

 brata, and (2) of the history of embryonic development. And it 

 is the distinct teacliing of both alike, that so far from the Cerebrum 

 being the fundamental portion of the brain (as its enormous relative 

 size in man would seem to indicate) it is originally a sort of offset, 

 from that axial cord which constitutes the primary and essential 

 part of the nervous apparatus of vertebrates ; the lower part of 

 this axis being formed by the spinal cord, and the upper by the 

 series of ganglionic centres which lie along the floor of the skull, 

 and which represent (in their relation to the sensory and motor 

 nerves of the head) the cephalic ganglia of insects. For in the 

 lowest fishes there is scarcely even a rudiment of the cerebrum, 

 the forward extension of the spinal axis constituting the whole 

 brain. And alike, as it would seem, in all vertebrates, the founda- 

 tion of the cerebral hemispheres is laid, not in these first-formed 

 "cerebral [or rather cephalic] vesicles," which really represent the 

 higher segments of the axial cord, but in a pair of minute 

 " vesicles of the cerebral hemispheres," which are budded off 

 from the most anterior of these. The proportion which the 

 development of the cerebrum, in the ascending series of verte- 

 brata, bears to that of the axial cord, corresponds so closely with 

 that which reason (so far as we can interpret its manifestations) 

 bears to instinct, as to warrant the conclusion that, since we are 



