132 



Biology in America 



western Kansas, which were once at the bottom of the old Cre- 

 taceous Sea. Traces of teeth still occur in the embryos of some 

 birds of the j)resent, a heritage from some ancestor of the 

 distant past. While Icthyornis still had teeth, it had pro- 

 gressed much further along the path of avian development 

 than Archffiopteryx in the structure of the hand. Nature in 

 her experiments is prodigal in the production of variations, 

 most of which she will never use in the development of new 

 species ; but once she is on the track of a useful variation she 

 becomes a strict conservationist and wastes no energy in the 



Hesperornis 



extinct diving bird with teeth, an inhabitant of the great Creta- 

 sea wliif h once covered our Great Plains. From Lucas, ' ' Animals 



Au 

 ceous 

 of the Past. ' ' 



Courtesy of the U. -b'. yatiuiuil Museum. 



maintenance of useless parts. So in the hand of the modern 

 bird and in Icthyornis as well, we find one of the fingers 

 being greatly strengthened for the support of the wing 

 feathers, and the others correspondingly reduced. The typical 

 reptile has five fingers, which in the modern bird are reduced 

 to one plus two rudiments, while Archa?opteryx had dropped 

 only two of his digits and still remained in possession of the 

 claws on his wings wliich the modern bird has dispensed with 

 as entirely out of date. There is however one conservative 

 member of the class who still retains a reminder of his rep- 

 tilian past in the form of a claw at the angle of the wing, 



