360 BIOLOGY AND ITS MAKERS 
velop they become successively more and more complex, 
and in their shifting history many rudimentary organs arise 
Fic. 108.—Fossil Remains of a Primitive Bird (Archeopteryx). 
From the specimen in the Berlin Museum. (After Kayser.) 
and disappear. For illustration, in the young chick, devel- 
oping within the hen’s egg, there appear, after three or four 
