284 SHULL— GERMINAL ANALYSIS [April 23, 



protoplasmic constitution and the '* mechanism " of heredity, which 

 has been totally unattainable by other means. 



In making analyses of such hybrid progenies and in working out 

 the nature and delimitations of the unit-differences involved in 

 Mendelian crosses, no assumption need be made as to the ultimate 

 nature of the " genes "^ or determiners. The attitude of nearly 

 all experimenters in the field of genetics is one of more or less con- 

 sciously suspended judgment on this point, and I believe that no 

 other attitude is justified at the present time. So far as I am aware 

 no investigator of the Mendelian phenomena " sees only particles " 

 as Dr. Riddle- has erroneously assumed, although it must be con- 

 fessed that his speech does sometimes seem to symbolize them. 

 The Mendelian interpretations do not " stand as a formidable block 

 in the path of progress," nor as any block at all, since all terminology 

 is more or less symbolic, and comes to mean new things as rapidly 

 as new truths are brought to light. All investigators in this field 

 will be appreciative of the service Dr. Riddle has performed in 

 bringing to their notice the recognized facts in the process of mel- 

 anin formation, though they can scarcely fail to regret his un- 

 familiarity with the present state of genetic science, and with the 

 attitude of those engaged in the investigations. If he had been thus 

 familiar with work in genetics, he might very easily have shown that 

 the facts of melanin chemistry are in harmony with the mass of 

 other data for which the " Mendelian interpretation " has proved 

 so illuminating. 



Although the question of epigenesis versus preformation is em- 

 phasized as a fundamental dift'erence between Riddle's views and 

 those of the Mendelians, this supposed difference is mainly imagi- 

 nary. Riddle's assumption of different " strengths " in the germ- 

 cells as a possible method of accounting for the production of differ- 

 ent colors or other characters in adult animals, involves a preforma- 

 tion of the same order as that assumed by the investigators of 



^ The genes are the differences, of whatever nature, whose existence in 

 the germ-cells determines the capacity of the unit-cha^'acters to be present 

 or absent in the individuals developed from those germ-cells. 



^Riddle, O., "Our Knowledge of Melanin Color Formation and its 

 Bearing on the Mendelian Description of Hereditj-," Bio!. Bull., 16 : 316-351, 

 May, 1909. 



