THE MUTATED GENE 215 



to the view taken by Sinnott and Dunn (1935), who cite an addi- 

 tional case from their laboratory (kinked tail in mice, after 

 Kamenoff (1934)). 



But information is also available for animals that suggests 

 that the genie control of differential growth is one of the 

 means of pattern production by simple effects of genes upon one 

 process with the consequence of an automatic patterning. 

 Among the phenocopies that Goldschmidt (1929a, 1935a) 

 produced in Drosophila by heat shocks was one that consisted of 

 a change of the wing shape into a lancet form; all transitions 

 from normal to lancet shape could be produced, apparently as a 

 result of the establishment of a new differential growth in 

 length and breadth of the wing in favor of length. In this case, 

 only the second phase of growth, by enlargement of cells, has 

 been involved, and mutants of this type are not yet known (?). 

 But the simple quantitative increase of the heat effect in the 

 series of types suggests a rather simple change of rate of some- 

 thing as the basis for the production of the different shape. 



Another case, in which the genetic side is also known, is the 

 case of the Bar eye in Drosophila according to Hersh (1928). 

 It is known that the eye of Drosophila (and other Diptera) is 

 — visibly or invisibly — subdivided into dorsal and ventral lobes. 

 In the Bar-eye mutants, these lobes become clearly visible. 

 Hersh found that the temperature effects upon the eye are differ- 

 ent in both lobes, the ventral lobe decreasing at a faster rate with 

 a rise in temperature. A statistical study of the data for different 

 genetic compositions led to the conclusion that formation of 

 facets (or destruction of facet-forming substance, Author) occurs 

 according to Huxley's equation for heterogonic growth. As the 

 ommatidia are differentiated in the optic disk primarily by an 

 induction from the brain (see page 34), the growth pattern 

 (ventral and dorsal lobe) may be the consequence of a gradient 

 (determination-stream, Author) or of a primary inductive differ- 

 ence. However this may be, Hersh concludes that the genes 

 of the Bar series produce their effects by altering the distribution 

 of growth in the developing zygote. As he finds that Ultrabar 

 larvae grow faster, it may be assumed that the facet-forming 

 reaction will have a different time relation to the general curve 

 of growth. "The manner of action of genes which affect the 

 size of the eye, as determined by the number of ommatidia, would 



