THE EYK AND OPTIC TRACT IX NORMAL AND 

 11 EYEL KSS ' ' DROSOPII TLA. 



MILDRKU HOGE RICHARDS AXD ESTHER V. FURROW. 



(Contribution from the Zoological Laboratory t Uni\i:-it\ { Oklahoma, Second 



Series. No. 48.) 



On of tin- most interesting mutations that has occurred in 

 Dn^ophihi mcl<inogaster is known as "eyeless." It was first 

 ob-ei \ed by the senior author in 1913, when MHIK- Hie- \\ith eyes 

 entirely wanting on one or both sides appeared in the culture-. 

 Tin- inln-rit.inre of eyeless was worked out at th.it time .nid the 

 e which is responsible for the condition \\a- loc.ited in the 

 fourth < hmmosome. Tlie stock breeds true to tin- c\cle con- 

 dition, but there is no fixed type of eyele^. It seems verj 

 probable th.it while the known gene in the fourth rhrom..-. nm- 

 determines that the eye shall be reduced, other genes ni >et 

 Inc. iti-' 1 ^"\i-rn the extent of the reduction of tli> 



Kei entl\ I ittle and Jones have carried on .1 selei ti< m < >\ e\ el< 

 Ilic^ in order to obtain races showing large and small propm-iion 

 Some progress was made and races o" these two kind> 

 ucie ~-|i.irated. These results may indicate .1 genetic ilitU-rem e 



bet \\eell the tWO lines. 



The name "eyeless" was perhaps incorre< tl\ applied, >im t- all 

 the Hie.- nf the pure stock are not entirely without e\ t -. 1'here i- 

 eiinsiderable \ariation in the size of the e>e. Xelen\ ha> found 

 t hat the e\ t ( .f a normal fly of certain strains \\ hich he had under 

 Hive-libation i ontains from 800 to 840 ommatidia. In the 

 less -t"ck the eye may be totally wanting, or it may appear 

 MiperlicialK to be normal in every particular e\ ept >i/e. e\'en at 

 it- maximum Iteinv; Mii.dler than the eye of the m-rmal \\ ild t\ pe. 

 Bet \\i-en these tu o extremes all gradations appear. Furthermore 

 there is usually in eyeless an entire lack of symmetry between the 

 eyes of the two ^ides. Sometimes the eyes are about equal in 

 size, sometime- present on neither side, and sometimes there will 

 be a fair -i/el e\ e on one side while on the other there will be only 

 a small one or none at all. 



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