248 



GENERAL BIOLOGY 



preserved, are the forms that are least instructive as to 

 genetic relationships. But, notwithstanding these things, 

 the record is clearly one of progress in differentiation of 

 parts and in complexity of organization. Seed plants and 

 back-boned animals are absent from the older strata of the 



earth's crust. 

 The forms at 

 present living 

 are most like 

 the later fossils, 

 and the farther 

 we go back 

 among the older 

 strata, the more 

 unlike existing 

 forms do the 

 fossils become. 

 Synthetic types 

 abound: i. e., 

 forms combining 

 characters of 

 two groups that 

 are in their liv- 

 ing representa- 

 tives sharply 

 separated. Such 

 a type is the 

 famous Arche- 

 opteryx (fig. 

 153) whose dis- 

 covery brilliant- 

 ly fulfilled Hux- 



FIG. 153. Archaeopteryx (after Zittel). d, clavicle; ^Y' 8 prediction 

 co, coracoid; sc, scapula; h, humerus; r, radius; , fhfl<;pH nn 

 ulna; c, carpus; 7, //, III, IV, digits. ^OaSCd OH 



