"THE COMING OF A BACKBONE 25 



modified to form piercing or sucking mouth-parts. Three 

 preoral segments carry the large facetted eyes, and a pair of 

 antennae; organs of feeling, often also of smell and hearing. 

 Originally every segment had its nerve-center or ganglion. In 

 insects the ganglia of the three preoral segments of the head 

 are fused in what we must call a brain sending its nerves to 

 antennae and to genuine visual eyes. The antennae are very 

 sensitive organs; the eyes are often very complex giving clear 

 and sharp vision of objects at some distance. The insect is 

 well aware of what is godng on about it. 



Insects evidently live on a distinctly higher plane of life 

 than any of the forms which we have previously studied. 

 Coelenterates are stationary or scarcely more than floating 

 and drifting animals, and we can hardly speak of muscular 

 and nervous systems. Lower worms crawled slowly but de- 

 veloped steadily muscle and nerve. Insects devote only about 

 half oi their body to the vegetative organs. The thorax is 

 purely locomotive, and the front half of the head entirely 

 sensory and nervous. This is progress which almost amounts 

 to a revolution. Hence in all insects we find very highly de- 

 veloped instincts, and some intelligence in bees and wasps, 

 which have also developed a high grade of social life. In- 

 sects are a very promising group; we naturally expect great 

 things of them. 



They were Nature's precocious children, made rapid prog- 

 ress, and had advanced far in early palaeozoic time. Their 

 development culminated with the appearance of bees and 

 wasps in Mesozoic or early Cenozoic time. Since that time 

 their progress seems to have ceased. This is a strange fact, 

 which demands careful attention. 



The external locomotive skeleton is admirably fitted to an 

 animal of small size. To encase an animal of the size of a 

 dog in such firm armor would surely hinder locomotion; it 

 would be difficult to frame the joints, and the successive moults 

 required to meet the growth of the body would be impossible. 

 We have seen the great advantages of small size; it has also 

 its marked limitations. The small insect could never hope to 



