A MUTATION IX THE MOTH-LIKE FLY. 13! 



necessitate the postulating of a determiner for pigment in each 

 phase. This series of pigmentary phases greatly facilitates the 

 \v<rk of identifying progeny since specimens may be positively 

 identified as normal or mutation in larval, pupal or adult 

 jes. 



In s< -es of inheritance the determiiu r for a character 



(! it - not become expressive except at a single stage- in the develop- 

 ment of the animal. Usually it is in the adult sta;,;e th.i 

 determiner shows its influence. The determiner must necessarily 

 be | ire -en t in .ill stages up to the time of its ex; n but may be 



.rded .is only a potential influence until the proper time is 

 hed. It is interesting to note that in the pn the 



determiner exerts its influence at three separated in the 



animal's life history; in the formation of the ocelli, in the de\ elop- 

 nient of the Malpighian tubules and finally in the formation of the 

 ipound eyes. This would indicate that sonu- ^i-ncral meta- 

 bolic process was being interfered with whenever that pro 

 was operating. In this particular case, then, the determiner 

 illicit be described as a regularly inherited "inllueiuv" upon the 

 nietabolie processes which are necessary to the elaboration of the 

 reildish brown pigment. 



1\ . MKTHOD OF TRANSMISSION OF NON-PIGMENI i \> ( '< >\UITION. 



\\hen it was first discovered that white-eyed mutants were 

 appearing in a mass culture the culture was closely watched and 

 the mutants were isolated as they appeared. l ; n>m the number 

 appearing it became evident that the L;encr.ition in 

 which they had been discovered was not the one in which they had 

 arisen. It is quite probable that one of the specimens first -een 

 and confined in the jar was a white-eyed individual which had 

 copulated with one or more of the normal specimens confined 

 with it. 



Tlu- mas- (iilt are in which the mutants arose would in such a 

 e be a mixture and without knowing the method of inheritance 

 of the mutation it would be impossible to know whether either 

 brown- or white-eyed specimens were homozygous for the 

 character in question. Neither was it known whether the 

 variation would be permanent and heritable or whether it would 

 prove to be a fluctuating variation. 



