No. 551] THE MENBELI AN NOTATION 653 



head variation. It apparently arose suddenly. He calls 

 it a mutation. 



The only result that can be considered seriously from 

 the standpoint taken in this paper is the result when se- 

 lecting for a rudimentary eye. Daphnia has been dis- 

 tinguished from Hyalodaphnia by the presence of a rudi- 

 mentary eye. The distinction does not seem to be valid, 

 for Woltereck noticed rudimentary eyes several times in 

 pure line cultures of Hyalodaphnia and they have also 

 been seen by others in wild cultures. He regards the 

 phenomenon as a reversion to a preexisting condition. 

 He found that the presence of the rudimentary eye is 

 periodic. In the spring it appears, in the summer it 

 again disappears. Either kind can produce progeny of 

 the other kind. From this fact it seems reasonable to 

 believe that environment or generation number has much 

 to do with the expression of the character, although 

 Woltereck in one place inclines to the opinion that ex- 

 ternal factors affect it but little. He performed several 

 experiments on the effect of light and temperature, how- 

 ever, and says that provisionally they gave no result 

 free from objection — " . . . gegaben einstweilen kein 

 einwandfreies Eesultat." Almost any interpretation 

 can be given this statement. 



Prom a pure line in which this variable eye spot ap- 

 peared, he isolated a mother and grandmother with the 

 character well developed. Ninety per cent, of the 

 progeny had the eye well developed. The rapidity of his 

 results and the fact of periodicity in the expression of 

 the character makes any cumulative effect of selection 

 exceedingly questionable. One is not justified therefore 

 in accepting it as proof without corroboration. 



Conclusion 



In conclusion, it may be asked if it is not reasonable 

 to accept simply as a nomenclature the description of 

 the whole facts of inheritance in sexual reproduction 

 given by the Mendelian system? Is it wise to turn back- 

 ward and to give up this handy and helpful notation 



