246 



PHYSIOLOGICAL GENETICS 



ignorance regarding the actual situation of the sensitive period, 



after the end of which the pattern cannot be changed. In recent 

 years, Kuehn, Henke, and their .students have successfully 

 attacked this problem. 



These experiments are partly based upon an interesting prog- 

 ress in the study of the morphology of such patterns, due to 

 Schwanwitsch (1924-1929) and Sueffert (1925-1929). These 



12 24 36 



60 72 84 % 12 24 36 



60 72 



(a) (b) 



Fig. 53. — Sensitive periods for the dark pattern elements in flour-moth pupae. 

 R, number of dark scales in the marginal spots; M, in the central spot; Q, the 

 dark bands; S, the "shadows." Abscissa: age of pupa in days and in fractions 

 of whole length of pupal period. Ordinate: units of the controls. O = M of 

 the controls. {From Kuehn and Henke, 1936, Abh. Ges. wiss. Goettingen, 15, 

 Fig. 87.) 



authors showed that within a given group of Lepidoptera (nym- 

 phalids, Schwanwitsch, Sueffert ; saturnids, Henke (1928, 19336, c, 

 1936), the wing pattern may be reduced to a simple arrangement 

 of elements that are invariably found. Figure 36 showed diagram- 

 matically such a case; the central field of symmetry with the 

 two symmetrical bands is noticeable. Outside lies the ocellar 

 system, followed by the marginal bands. Near the roots of the 

 wing are the so-called hollow elements. 



Sueffert (1925) and Kuehn (1927) further showed that in 

 temperature experiments these different "fields" reacted inde- 



