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THE POPULAR SCIENCE MONTHLY. 



animal, whether they be constant or temporary ones. In order to dis- 

 play this property it is necessary that sensation should exist, and that 

 this should be pleasurable or painful, in order to produce a determinate 

 movement to increase the one or escape the other. This is the basis of all 

 design, for without consciousness there can be no design. Just where 

 this consciousness first displays or displayed itself in living things it is 

 not possible to know at present with certainty, but its first exhibition 

 was probably in the pain of hunger. The first designed act was, then, 

 the taking of food. The first structure was, therefore, also some kind 

 of arrangement for seizing and surrounding food. This having been 

 performed, another set of functions had its birth, one which was destined 

 to follow all new experiences, and in turn to dominate all later acts. 

 This is the memory of the act and of its consequences, which remains 

 as the basis of mind. An impress once, made on consciousness is not lost, 



because it has modified the molecular 

 structure of some part of the living 

 material in a way as yet unknown to 

 a us. The movement which results from 

 this memory is the first designed act, 

 and this also affects structure, and 

 produces the first motor link between 

 mind and body, as the first stimulus 

 & perceived produced the first sensory 

 link. From this time onward the law 

 of use and effort has its way. Its first 

 result is to build a mind-machine, or 

 nervous system, or its equivalent. This 

 kind of building has evidently preced- 

 ed all others in time, and its latest and 

 highest product is the human brain. 

 The evidence of vertebrate paleon- 

 tology places this statement beyond 

 the stage of mere hypothesis. We 

 have learned that, with a few minor 

 exceptions, the brains of the verte- 

 brata, and especially of the mammalia, have greatly increased in 

 complexity and in size with the lapse of geological time. This is il- 

 lustrated by the accompanying figures of the brain-chambers or casts 

 of brain-chambers of two ancient and one late Tertiary mammals. The 

 Coryphodon elephantopus is the largest animal of the three, and the 

 Phenacodus primcevus, of which the skeleton was figured in the pre- 

 ceding article, is a little smaller than the Procamelus occidentalis, the 

 third species. The last is the latest species in time, and is one of the 

 ancestors of the existing camels and llamas. The much greater size 

 and complexity of the brain, and especially of the cerebral hemispheres, 

 as compared with the two other species, are striking. 



Fio. 8. Cast of Bkain-Cavttt of Phena- 

 codus riiiM^Evus, showing small hemis- 

 pheres : a, side ; b, from above ; c, from 

 below. One half natural size. (From 

 Wyoming ) 



