xviii PAST HISTORY 355 



These are but a few of the great events of animal 

 evolution, but enough perhaps to prompt the student to 

 develop further an interesting line of inquiry. 



One of the most general results of evolution is complexi- 

 fying. Things become more intricate. This is true of 



j 



the inter-relationships that become established in the 

 web of life ; the threads make more intricate knots in 

 the economy of birds than in that of sponges. It is 

 true also of behaviour; the big-brained mammal sym- 

 bolised in Brer Rabbit is a subtle creature, and even the 

 low type of brain-development represented by bony 

 fishes belongs to a different epoch from the medusae under 

 whose umbrella they shelter. It is true also of the 

 internal economy of the body, which is more intricate 

 in an insect than in a polyp, in a bird than in fish. As 

 we ascend the series, the varietv of internal activities 



- 



increases there are more different kinds of metabolism 

 -and the subtlety of correlation increases. The different 

 processes work more perfectly into one another's hands. 

 Finally, the tendency to complexify is seen in structure, 

 where we have to do with the other side of the complexi- 

 fying of function to which we have just alluded. It is 

 important to realise, however, that the structural com- 

 plexifying which counts in evolution is in the direction 

 of increased organisation. The architecture of the 



o 



flinty skeleton of Venus's Flower Basket (Euplectella) 

 is intricate, yet it does not amount to much more than 

 the endless repetition of a certain kind of scaffolding. 

 Its intricacy is quite different from that of the cortex 

 of a dog's cerebral hemispheres, in which innumerable 

 nerve-cells, with complex interrelations, are organised 

 into a unity. In the quaint masticatory, respiratory, 

 and locomotor apparatus know r n as Aristotle's Lantern 

 in sea-urchins, there are twentv-five or more calcareous 



/ 



pieces, but this sort of complexity, finely as it works, is 

 on a relatively low plane compared with that of, let us 

 say, a dog's head. We would advise the student to give 

 reality to his impressions by securing practical familiarity 

 with some representative specimens of complexity of 

 structural organisation (see fig. 115). 



