DROSOPHILA BRED IX THE DARK. 299 



\Yith these precautions it was found that offspring of different 

 parents within the same strain, those bred in the light as xvell 

 as in the dark, vary considerably in their reaction-. Further, 

 this difference does not seem to be due to inheritance from the 

 parents. To tesi thi- I selected five Hie--, each <>i which failed 

 to pass through the tube in five minutes. Tin- next day, I 

 retested the-e -aim- fi\v flies and again they failed to react. 

 This sluggishness \va- not due to poor development, a- tlu-v looked 

 Strong and vigorous. These five (lie- \\etv bred and their off- 

 -pring tested. The avi Mine of tin,-.- \\hich passed through 



the tube and the percentage which fail<-d was approximated 

 tin- same as tor tin- MTU--, indicating that -omelhing other than 

 inheritance i- ih< cause "I" thi- differem v in reaction. 1 h.i\e 

 taken t\\o pair-, brother- and sisters, f-d them on tin- -ame food, 

 kept tin in -ide by -ide in tin- -aim- room and yet tlu-ir offspring 

 -li'iucd a decided din. in their reaction- to light. This 



fact has caused m< >t -leal of trouble and led to the eiTO- 



neouscon< eption -tated in the pre\ ion- note. In fat t I can obtain 



the -ame re-nli between the offsprii lifferenl parents in the 



same Strain \\hidi I formerlx -tated \\a-obtained b\ c, .mp.iring 

 Ilie- bred in the dark \\ith tho-r bred in tin- light. Often this 

 dillen i -I that it i- noticeable before the llie- are 



ted, thi a-t beJDg more ea-il\ e\ciiei| b\- handling. 



I OD!\ possibl thi- dilieren.-e \\hich 1 have to 



i- liie food, a- it max '.in. nt degrees of lennentalioD 



after it i- placed in the xial. Another thing which lead- me to 

 beliexe thai the |od max be the uiiderlx ing caii-e i- thai the 

 la-t the- taken Irom anx one xial are u-u.illx more -higgi-h than 

 the lit.-t one I .en \\ith thi- differi'iici- in the reaction- of 



tile Offspring Oi litlel III parent-. I belieXe the reacticiD- of I.O.KI 



individuals trom manx dillereni jiarent- gives .1 close approxi- 

 mation to the average for the -train. 



The lollou ing table gives the axerage t ime of t he the- in pa itrj 



i.cx- i- in 



I thi- I 'ite. 



i : -'5. i per i-t-iit. 



l : . lid-. Ml. 



Sen. } No. 3 i 'iuls. nt. 



n-l-. r cent. 



