102 THE SHORTER SCIENTIFIC PAPERS 



Castle, Carpenter, Clark, Mast and Barrows ('06) 

 made observations on the variability and fertility of 

 Drosophila a-mpelophila Loew, the small fruit fly, as modi- 

 fied by inbreeding and cross breeding. They found that 

 "inbreeding does not affect the variability in number of 

 teeth on the sex comb of the male, nor the variability in 

 size." While the conclusion is not in accord with an earlier 

 observation (p. 780) that variability would seem to have 

 been increased by inbreeding so far as a comparison of 

 the sixth inbred generation with the sixty-first genera- 

 tion, the small number utilized in the sixth generation 

 (40 males in series A-6, B-6, C-6 each) was ground for 

 the opinion that such a conclusion had little value in com- 

 parison with data pointing in the reverse direction. If 

 however we calculate the coefficient of variation for the 

 length of the tibia, an unfortunate omission on the part 

 of the writers, it may be noted that the flies produced by 

 inbreeding are decidedly more variable than those pro- 

 duced by cross breeding. Data for this conclusion are 

 given in a subsequent part of the present paper. 



Walton ('08) noted that the results of measuring zygo- 

 spores of Spirogyra indicated that the close-bred indi- 

 viduals were more variable than the cross-bred individuals 

 and furthermore that the data went far toward confirm- 

 ing the theory that sex existed for the purpose of limiting 

 instead of augmenting variability. 



Emerson ('10) found that crosses between races of 

 plants (maize, squash, beans, gourds) differing in size and 

 shape had the variability of the second (F2) generation 

 approximately twice as great as the variability of either 

 parental form or of the first (Fi) generation. This he 

 explained on the basis of the segregation of size and shape 

 characters. Similar results were obtained by East ('11) 

 for maize and Hayes ('12) for tobacco. 



Jennings ('11) extending and summarizing his breed- 

 ing experiments on Paramecium concluded that 



The progeny of conjugants are more variable, in size and in certain 

 other respects, than the progeny of the equivalent non-conjugants. 

 Thus conjugation increases variation. 



Later ('13) continuing his investigations he stated that 



conjugation increased the variability in the rate of repro- 



