40 rilYSlol.oCKAL <i EMETICS 



mutant genes, the effect of which must be to stop further differ- 

 entiation at definite points and at a definite time or to retard it 

 so that it cannot be completed. The following example shows 

 such a process actually both in the form of a genetic effect and 

 in the form of a phenocopy (Fig. 15): In low-grade male intersexes 

 of bymantria dispar, the part of the genital armature called 

 uncus becomes paired, a transition from the unpaired male 

 condition to the paired female homologous structure (labia), and 

 this intermediate condition is caused genetically by a definite 

 genie combination. Kosminsky (1909, 1924, 1927) and later 

 Goldschmidt (19226) showed that this same condition may be 

 produced by action of cold upon young male pupae, and Bobroff 

 produced the same effect by X rays (1930). Kosminsky further 

 showed that the uncus in the male is first laid down as a paired 

 Anlage which later concresces; the treatment at the proper time 

 prevents concrescence just as the intersexual genetic condition 

 does. Another case of this type is the eye abnormality called 

 coloboma, consisting of incomplete coalescence of the eye bulb. 

 This occurs as an inherited anomaly and may also be produced in 

 rabbits by feeding turpentine to the pregnant mother. 



The analysis of this and similar cases, a considerable number of 

 which are found in the different organs in case of intersexuality, 

 furnished many facts, which demonstrate that an embryonic or 

 developmental stage of an organ may become perpetuated in the 

 adult as a consequence of definite genetic conditions which 

 generally are of the same type as a mutation (here a mutant 

 condition of sex genes). We shall therefore not be surprised to 

 find that frequently a mutant type is identical with a develop- 

 mental stage of the Wild type. As examples, I mention the work 

 of Tammes (1934). She found that in Linum usitatissimum, a 

 number of genotypes may be isolated that are distinguished by 

 different grades of coloring of the seeds, in fact different steps 

 of the spreading of color around the seed. A study of the 

 development of coloration in normal seeds showed that all 

 the conditions found in the different mutant genotypes reappear 

 as stages of normal development in which color first appears at 

 the pointed end of the seeds and spreads along the edge to the 

 broad end of the seed. Both faces of the seed remain light. 

 Then this light spot is more and more restricted until the whole is 

 self-colored. Tammes also realized that the explanation of this 



