398 GREAT STEPS IN ORGANIC EVOLUTION 



bral cortex, which is the chief seat of intelligence. It covers, 

 if spread out' about a foot and a half square and is said 

 to consist of about 9,200,000,000 nerve-cells, which are in- 

 tricately connected together. Apart from supporting tissue 

 and blood-vessels, these cells and their processes would only 

 occupy about a cubic inch and weigh 13 grammes, but they 

 form the material theatre of our intellectual life, and it is 

 practically impossible to exaggerate the complexity of inter- 

 relations, — a complexity on a different plane altogether from 

 that of the Venus's Flower Basket. In the sea-urchin there 

 is, as Aristotle knew, a quaint piece of intricate skeleton, 

 the lantern, which has masticatory, respiratory, and actually 

 locomotor functions. It is a very fine contrivance, which 

 works very beautifully; it consists of twenty-five or more 

 different calcareous pieces and is worked by numerous mus- 

 cles. But this sort of complexity, finely as it works, is on 

 a relatively low plane compared with, say, our eye or ear — 

 where organisation reaches its zenith. 



But the organisation of structure which increases through- 

 out evolution, except in cases of retrogression, is correlated 

 with a complexifying of the internal economy of the body. 

 The variety of internal activities increases, there are more 

 different kinds of metabolism, the subtlety of correlation 

 grows, the different processes work more perfectly into one 

 another's hands. Small bodies near the kidneys secrete 

 from part of their structure a potent substance called adren- 

 alin which is passed into the blood. The amount of adrenalin 

 in our blood is normally about one in 20,000,000 parts; 

 but if we suffer from righteous anger the secretion of adrena- 

 lin rapidly increases and like magic prepares us for struggle, 

 affecting the pressure and distribution of the blood, the 

 vigour of the heart, the amount of sugar in the blood, the 



