WORMS TO VERTEBRATES 



65 



to devote more material to building a larger brain. It 

 was better to build more muscle. But now with 

 stronger muscles at its command, and better sense- 

 organs to report to it, every grain of added brain 

 material is beginning to be worth ten devoted to 

 muscle. The muscular system will stiU continue to 

 develop, but the brain has begun an almost endless 

 march of progress. The eye becomes of continually 

 increasing advan- 

 tage and impor- 

 tance because it 

 has a capable brain 

 to use it ; and brain 

 is a more and more 

 profitable invest- 

 ment, because it is 

 served by an ever- 

 improving eye. 



The annelid had 

 hit upon a most 

 advantageous line of development, which led ultimately 

 to the insect. The study of the insect will show us 

 clearly the advantages and defects of the annelid plan. 

 First of all, the insect, like the moUusk, has an external 

 skeleton. But the skeleton of the mollusk was purely 

 protective, a hindrance to locomotion. That of the in- 

 sect is stiU somewhat protective, but is mainly, almost 

 purely, locomotive. It is never allowed to become so 

 heavy as to interfere with locomotion. In the second 

 place, the insect has three body regions, having each 

 its own special functions or work. And one of these is 

 a head. The annelid had two anterior segments differ- 

 ing from those of the rest of the body ; these may, 

 5 



UYBMELEO TOBMIOABlnS. ANT-LION. 

 FROM SCHMAKDA. 



1, adult ; 2, larva ; 3, cocoon. 



