194 THE WHENOE AND THE WHITHER OF MAN 



protection of tlie animal, and only gradually did it 

 become of much service in locomotion. Being deep- 

 seated it very possibly changed all the more slowly. 

 Furthermore, a cartilaginous rod, like the notochord, 

 even fully developed, hardly enabled the animal to 

 fight directly with the mail-clad crab. The internal 

 skeleton had to become far more highly developed be- 

 fore its great advantages, and freedom from disadvan- 

 tages, became apparent. The moUusk and crab were 

 working a mine rich in surface deposits although 

 soon exhausted. The vertebrate lead was poor at the 

 surface, and only later showed its inexhaustible rich- 

 ness. It looked as if the vertebrate were making a 

 very poor speculation. 



Whether this explanation be true or not, a glance 

 at a chart, showing the geological succession of oc- 

 currence of the different kingdoms, proves that in the 

 oldest palaeozoic periods there were well-developed 

 cuttlefish and crabs before there were any vertebrates 

 worthy of the name. If any Avere present, their skele- 

 ton was purely cartilaginous and not preserved. 



I think we may go farther, although in this latter 

 consideration we may very possibly be mistaken. 

 We have already seen that the progress made by any 

 animal may be measured more or less accurately by 

 the length of time diu-ing which its ancestors main- 

 tained a swimming life. The ancestors of the ccelen- 

 terates settled to the bottom first. Then successively 

 those of flatworms, mollusks, annelids, and crabs. All 

 this time the ancestors of vertebrates were swimming 

 in the water above. Food was probably more abun- 

 dant, certainly more easily and economically obtained 

 by a creeping life, on the bottom. But thither the 



