38 THE PROBLEMS OF EVOLUTION 



Harrison ^^ reports that limb buds of the sala- 

 mander, Amblystoma punctatum, when transplanted 

 to parts of the body other than their normal loca- 

 tion, frequently express their potentiality as they 

 would under normal conditions, by developing 

 into legs of normal appearance. 



Such observations indicate that there is some 

 latitude in the conditions which may activate a 

 given factor in the heritage, but we need only note 

 the extensive modifications produced in developing 

 embryos by relatively slight abnormalities of envi- 

 ronment to realize that the correlation is, in general, 

 very delicately adjusted. Morgan's monumental 

 volume. Experimental Embryology, records more 

 cases than are necessary to establish the point. ^^ 



Development which appears to proceed nor- 

 mally under abnormal conditions is relatively rare, 

 and in such cases as those cited above, close scru- 

 tiny shows that the degree of normality attained 

 is due to the persistence of adequate normal en- 

 vironment in spite of the artificial modification. 

 The salamanders' transplanted limb buds may 

 continue their development into limbs correspond- 

 ing to their original destiny, but not to the extent 

 of taking the place of normal legs in the individual 

 body. This much may be accomplished through 

 their reception from the blood stream, and from 



" Jn. Exp. Zool, Vol. XXXII, pp. 1-136, 1921. 

 13 Experimental Embryology, pp. xi + 766, 1927. 



