124 



Biology in America 



is impossible to distinguish by structure alone the two types 

 of bone. While the adults were terrestrial in habit they 

 nndonbtedly possessed aquatic larva? in many cases, as is 

 showu by the presence of gills in the fossil remains of the 

 latter, and their kinship to aquatic forms is clearly shown by 

 a groove in the dermal bones of the head, indicating the pres- 

 ence of a series of sense organs peculiar to fishes and known 

 as the lateral line organs. 



The Carboniferous period likcwis,' witnessed a great develop- 

 ment of nuiny other types of animal life, spiders, scorpions, 



p^-'-- 



J 



-«.*i 



An Imaginary Landscape of the Coal-Forming Period 

 Showing stegocephalans and a giant insect in the foreground, with 

 coal-forming plants in the background. After Williston, "Water Kep- 

 tiles of the Past and Present'' (adapted from Neumayr), 

 By permission of the University of Chicago Press. 



centipedes, insects and snails, while the plants indulged in 

 a veritable riot of luxuriant growth. 



We may perhaps picture to ourselves the conditions of the 

 evolution of land from water vertebrates in some such way 

 as this : With the gradual recedence of the sea and elevation 

 of the land extensive swamps were formed in which developed 

 a luxuriant vegetation consisting of giant club mosses, "horse 

 tail" and tree ferns and primitive representatives of our 

 modern pines and spruces. In the dense forests bordering the 

 stagnant pools, no touch of bright color was there to enliven 

 the monotony of the scene, for neither bird nor butterfly 



