70 



The Bird 



ply a copy of the primitive flakes or joints of the tiny 

 muscle-beginnings, and is comparable to the joints or 

 rings in the bod}' of a beetle, butterfly, or earthworm. 

 In a short time all the squares will fuse together, and not 

 until later will the}' separate again into divisions which 

 will ultimately form the real bones of the spinal column. 

 Every little chick, before it hatches, goes through the 

 same strange changes, — living reminders of the evolution 

 which has gone on in past ages of the earth. It is inter- 



FiG. 46.— Muscle-plates, or false vertebrse, of third-day embryo chick. 

 Magnified 25 diameters. 



esting to note that the vertebrse of the embryo chick 

 pass through a stage w^hen they are biconcave, — a condi- 

 tion found both in Amphioxus and Archseopteryx. 



This digression upon the back-bone history may seem 

 out of place, but in reality such a bird's-eye survey of 

 the past, imperfect as it is, will add a new interest to 

 our handful of chicken-bones. 



