THE MUTATED GENE 261 



a number of pattern elements to individual genes. As these 

 patterns may be combined in a single individual, just as such 

 wing patterns in Drosophila as miniature, beadex, expanded 

 may be combined in one wing, each element must be caused 

 by an independent embryological process. Therefore, in 

 these and similar cases (Lebistes, Winge), an analysis will 

 have to be applied of the type used for the wing of the flour 

 moth. No facts are yet known to warrant more specific 

 conclusions. 



We may finally give the list of types of pattern formation 

 as compiled recently by Henke (1936), adding such information 

 as is pertinent to our topic : 



1. Patterns based on chimeric development. These are the 

 patterns in gynandromorphs, chimeras, somatic mutations. 

 They throw light on problems of autonomous differentiation but 

 hardly on actual developmental patterns. 



2. Patterns based on rhythms in time. Here belong the 

 patterns of feathers, produced by hormone injection. Possibly 

 also patterns like feather pattern in Plymouth Rock. Their 

 relation to genie action is not yet clear. 



3. Crack patterns. These have not yet been mentioned. 

 Regular cracks, as in a shellac film or craquele china, have been 

 used by Hirata (1935) to explain regular patterns in beans. If 

 we substitute zones of different growth or tension for the cracks, 

 the consequences will be the same as for the latter pattern-form- 

 ing processes. 



4. Areas of diffusion from one center. Here belong the cases 

 of spotting, pterylae and their like. 



5. Field limits as pattern. Here belong the best analyzed 

 cases of the bands on the lepidopteran wing, determined by the 

 front of a determination stream. They are combined with a 

 pattern of differential velocity of differentiation. 



6. Rhythmic diffusion from centers. This is the Liesegang 

 ring type of pattern-forming process. 



7. Simultaneous rhythms. An instantaneous rhythmical ar- 

 rangement, e.g., by tensions in a membrane, producing zebra- 

 like patterns. 



8. Combination patterns. This is the Lepidopteran type of 

 pattern, composed of different areas with a combination of some 

 of the foregoing pattern-forming processes. 



