THE AMERICAN NATURALIST [Vol.LVI 



has necessarily been lost from the cell. The inheritance 

 complex of the germ is like goods in the piece ; it is only 

 as development progresses that the garment becomes 

 specified ; bnt above all, be it remembered that the finished 

 garment is of the same fundamental constitution as the 

 goods in the piece. 



It is a commonplace of experimental embryology and 

 experimental morphology, in fact, that the same initial 

 materials may yield ver\^ different end-products in dif 

 ferent environments. The phenomena of heteromor- 

 phosis, metaplasia, regeneration and regulation all attest 

 this. Blastomeres originally directed toward becoming 

 one part of an organism may be switched about to become 

 another part ; tissues originally subserving one function 

 may be turned to other uses ; ectodermal cells which by no 

 possible chance could have been predestined to form 

 crystalline lens will, nevertheless, form a lens similar to 

 that of the normal eye if stimulated by a transplanted 

 optic cup. Or, if the lens is removed from the eye of a 

 salamander, a new lens may develop from the edge of 

 the old iris, a part from which the lens never normally 

 develops in the embryo. In short, it is a well-established 

 fact in many organisms that cells occupied with the 

 specializations of one part of the individual still retain 

 the potentialities which would fit tliem to the functions 

 of some different part, and may, in fact, under exper- 

 imental conditions be made to redifferentiate into the 

 structures of another part. Such facts, togt'tlicr with 

 the exactitude of chromosome distrilnitioii in iiiitt»si> 

 indicate clearly that many, ])()>sihly all, colls of aii or- 

 ganism retain the hereditary tendeiK-ies that existed in 

 the original zygote. Because of limitations due to its 

 location in the organism, however, a given cell realizes 

 only a small proportion of its inherent possibilities. And 

 after all this is no more rcmarkal)le than the fact that 

 the .......or n....Hv..H,ara..t.rs,navshunl,.rindHinit,.lv 



in ir.TM, an<l .<.,na. .vn.ratiun aft.r ovn.ratl.m. nntil 

 con.litluns suitahle tor thrir ox,.n-..ion as .-lumu-ters 

 occur. 



But now, regarding heredity as in its simplest expres- 

 sion merely the passing on of metabolic activities already 

 established, and conceding that the distinctive structural 



