THE PHENOMENA OF MUTATION 175 



CEnothera, exemplified by our well-known Evening 

 Primrose. 



Professor T. H. Morgan informs us l that within 

 five or six years in laboratory cultures of the fruit- 

 fly, Drosophila ampelophila, arose over a hundred 

 and twenty-five new types whose origin was com- 

 pletely known. The first of these which he mentions 

 is that of eye colour, differing in the two sexes, in 

 the female dark eosin, in the male yellowish eosin. 

 Another mutation was a change of the third seg- 

 ment of the thorax into a segment similar to the 

 second. Normally the third segment bears minute 

 appendages which are the vestiges of the second 

 pair of wings ; in the mutant the wings of the third 

 segment are true wings though imperfectly developed. 

 A factor has also occurred which causes duplica- 

 tion of the legs. Another mutation is loss of the 

 eyes, but in different individuals pieces of the eye 

 may be present, and the variation is so wide that it 

 ranges from eyes which until carefully examined 

 appear normal, to the total absence of eyes. Wing- 

 less flies also arose by a single mutation. These 

 were found on mating with normal specimens 

 to be all recessive characters, thus agreeing with 

 Bateson' s views. The next one described is dominant. 

 A single male appeared with a narrow vertical red 

 bar instead of the broad red normal eye. When 

 this male was bred with normal females all the eyes 

 of the offspring were narrower than the normal 

 eye, though not so narrow as in the abnormal male 

 parent. It may be pointed out that this is scarcely 

 a sufficient proof of dominance. If the mutation 



1 A Critique of the Theory of Evolution (Oxford Univ. Press, 1916), 

 p. 60. 



