PAPERS ON BIOLOGY AND AGRICULTURE 181 



The work was done entirely with parthenogenetic fe- 

 males, no males appearing ; hence the results are entirely 

 in a pure line. Whether similar results will continue op 

 whether the difference will persist when selection is dis- 

 continued remains to be seen. The full significance of 

 the experiment can not be gauged in so early and pre- 

 liminary a stage. 



What the causes are which may produce selection in 

 a pure line if such should prove possible in the long run, 

 is still an open question. A. M. Banta in his interesting 

 work on "Selections in Cladecera on the Basis of a Phys- 

 iological Character" takes up the question. He was 

 slightly successful in selecting Daphnia longispina for its 

 reaction to light. In one line he got a difference 4.05 

 times the probable error. He thinks selection may be 

 due to (1) general physiological changes or (2) direct 

 genetic changes. The first consists of materials carried 

 over by cyloptasm, lide bacteria or protozoa or dye, 

 which fed to fowls appears in egg yolk (Riddle 1908). 

 But if the genetic basis be assumed, then he thinks that 

 selection in a pure line altho it cannot cause genetic 

 changes "may seize upon modifications of the character 

 used in selection as they occur and in the case of plural 

 genetic changes may build up differences between se- 

 lected strains" and may be "the means of utilizing the 

 variations in accomplishing the end sought." There is 

 no way in Daphnia by which there could be any recombi- 

 nation of nuclear material, since there is only one ma- 

 turation division without reduction in the partheno- 

 gentic egg. 



Banta also discusses the mutation theory. In connec- 

 tion with such small genetic changes he would not call 

 them mutations, but calls the point immaterial. He 

 would not call them segregations or larger mutations be- 

 cause they occur too often and because there is no chro- 

 matic reduction involved. Sturtevant, in his work on 

 Dichaet flies, was able to select plus and minus strain for 

 a number of bristles. Dichaets vary more in bristle num- 

 ber than non Dichaets. In his final discussion he raises 

 three questions. 



