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 body of a beetle, butterfly, or earthworm. 

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

 until later will they 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 ial>L> \eitebrse, of third-day embryo chick. 

 Magnified 25 diameters. 



esting to note that the vertebrse of the embryo chick 

 pass through a stage when 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. 



