A VIEW IN PERSPECTIVE. 143 



soft parts. An internal skeleton was developed. 

 This first appeared as a soft but resisting rod (noto- 

 chord), inside of the back, and reaching from head to 

 tail. This rod gave some strength, but could not 

 become resisting without destroying the flexibility 

 of the body. Therefore it soon became broken into 

 segments to give the body flexibility, and then it 

 hardened into a series of bones and formed the spinal 

 column and the basis of an internal skeleton. Of 

 this early history we have no trace from fossils, for 

 it was not until this rod had hardened into cartilage 

 that it was possible for vertebrates to be preserved 

 in the rocks. The early history of the vertebrates, 

 therefore, must be read from embryological evidence. 

 This type of an internal skeleton immediately proved 

 to be a success. This means of support gave strength 

 and rigidity to the soft parts, and at the same time 

 did not burden them so much as to render them 

 unwieldy, for it was adapted on mathematical prin- 

 ciples for furnishing the greatest strength with the 

 least bulk. 



The value of this skeleton immediately showed 

 itself by the increase in size of the animals possess- 

 ing it. We find that there followed now a new 

 phase of animal history. For a long series of succeed- 

 ing ages we see an increase in size among the higher 

 members of the animal kingdom. Doubtless these 

 early vertebrates had fierce contests with other ani- 

 mals, but the large and active vertebrates soon 

 proved themselves superior to the clumsy mollusks 

 and the sluggish trilobites. The struggle of verte- 

 brates with each other was severe. Size was a factor 



