yo 



The Bird 



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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, butterfl}-, 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 vertebrte, of third-day embryo chick. 

 Magnified 25 diameters. 



^' 



esting to note that the vertebra* of the embr3^o chick 

 pass through a stage when they are }>iconcaA'e, — a condi- 

 tion found both in Amphioxus and Archseopterj^x. 



This digression upon the back-bone history ma}" seem 

 out of i)lace, 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. 



