14 BIOLOGICAL LECTURES. 



dealing with a portion of the resulting structure, viz., the 

 shell, we are dealing perhaps somewhat more directly with 

 the influence of heredity and its vehicle than we would be, 

 if the subject of our discussion were a more distant somatic 

 product, such as a bone or a feather. 



The relation of the ovum to the complete ^g^ is practically 

 the same as that of a "caddis-worm," to its "case." The 

 preferred material may be bits of straw, but, in the absence of 

 straw, small pieces of wood may be made to answer. The 

 "worms" in the "cases" of wood are themselves not different 

 from their, perhaps more fortunate, neighbors in straw " cases." 

 It is only when they adopt the wood in preference to the straw 

 that an ontogenic makeshift becomes a phylogenic variation. 

 New building material does not make a new architect. 



In America the materials supplied for the developing ovum 

 are different from those supplied in England, and the resulting 

 structure is consequently different. To what extent the new 

 materials have won the favor of the keimplasm cannot be deter- 

 mined by merely allowing American birds to breed again in 

 England, for in England there would be a prejudice in favor of 

 local material, and under the revival of an ancient environment 

 palingenic variation might also deceive. Both English and 

 American birds should be placed in some third locality which 

 combines equally or eliminates the prejudicial environmental 

 conditions of the two countries. Then, and not until then, 

 shall we know to what extent the ontogenic variations in either 

 country have really become phylogenic. 



