HISTORY OF ZOOLOGY. 



33 



cephalopods, outlines of medusae) preserved in the rocks. Even 

 the hard parts remain connected only under exceptionally favor- 

 able conditions. If further we take into consideration the fact 

 that these treasures are buried in the bosom of the earth, and are 

 usually obtained only by accident, in quarrying and road-build- 

 ing, and besides only extremely seldom excavated with scientific 

 care, it becomes sufficiently clear how little is to be expected from 

 the past and indeed future material of paleontology. 



Examples of Paleontological Proof. Yet paleontology has 

 already furnished many important proofs of the theory of descent. 



Fio. 2. Archceopteryx lithnijraphica. (After Zittel.) cl, clavicle; co, coracoid; 7i, 

 humerus ; r, radius; w, ulna ; c, carpus ; I-IV, digits ; sc, scapula. 



It has shown that the lower forms appeared first, and the more 

 highly organized later. Among animals in general the latest to 

 appear were the vertebrates, and of these the mammals; among 

 the mammals man. For smaller groups genealogical material has 



