LAND LIFE BEGINS 39 



cousin among the early plants. It grew to a height 

 of forty or fifty feet, ordinarily, and sometimes to 

 nearly a hundred feet ! It was an age of giants. Club 

 mosses ran to a height of a hundred and fifty feet; 

 and even tree ferns sometimes spread their graceful 

 dark green canopies at fifty or sixty feet above the 

 soil. 



The animals had meantime followed the vegetation. 

 Their skeletons or shells are now buried in the soil, 

 which has become our rocks, and we can fairly trace 

 the invasions from the sea. Snails were among the 

 earliest arrivals. Worms of various kinds became 

 adapted to land life. Presently we find traces of 

 insects — "primitive bugs" and "primitive cock- 

 roaches," to translate the learned names which are 

 given to them. There is in South America and a few 

 other places to-day a very primitive little creature, 

 called the Peripatus, which you would take to be 

 a very strange caterpillar if you met it in the wood. 

 It is one of the beings of the remote past, which has 

 somehow survived the struggle of ages, and it helps 

 us to understand the origin of the insects. Apparently 

 some of the worm-like creatures which invaded the 

 land from the sea developed tubes in the skin (a sort 

 of tiny "lungs") for breathing air. They flourished, 

 and, as is almost always the case with these large 

 prosperous families, they scattered and evolved in 

 various directions. From them, we think, in the 

 course of time, came our insects, spiders, scorpions. 



