THE MUTATED GENE 



241 



4. Composite Patterns. — Considering rather simple types of 

 patterns, we discussed cases where the limiting factor for the 

 spreading of a determining stuff was given by a pattern already 

 present in the system, e.g., the zigzag bands of the Lymantria 

 wing. The analysis of the effect of mutant genes will more 

 frequently meet with the simpler type of the processes because 

 Mendelizing genes affect more often late details of morphogenesis. 

 But analysis of more complicated cases of pattern has also 

 yielded considerable insight. Thus far, however, it has not 



Fig. 49. — Pupal wings of intersexual males of Lymantria dispar after drying, 

 showing the finished white scales and the soft collapsed scales in the later dark 

 parts of the wing. {From Goldschmidt, 1923, Arch. mikr. Anat. 78.) 



been possible to fit all the partial processes that have been found 

 into one simple coherent picture. The attack upon this problem 

 has been done entirely with the Lepidopteran wing as material, 

 except for a few facts relating to mammals. There are two types 

 of facts of primary importance which thus far could not be 

 properly linked, though this is required for a full understanding 

 in the study of the lepidopteran wing. 



a. General Embryological Features. — In studying the develop- 

 ment of patterns in the lepidopteran wing, Goldschmidt (1920c?) 

 found one general rule which may be stated as follows: A long 

 time before pigment is formed and before the scales are perfected, 

 a different rate of differentiation becomes visible in regard to the 



