LEE BARKER WALTON 87 



any desire to be critical and at some risk of exceeding the 

 controversial bounds which a paper of this nature allows, 

 a few of the more important investigations touching upon 

 the subject will be considered. 



Castle, Carpenter, Clark, Mast and Barrows (1906) in 

 a series of observations as to the effect of cross breeding 

 and close breeding on the variability and fertility of the 

 small fruit fly, Drosophila ampelopbila Loew., stated that 

 "inbreeding did not affect the variability in the number 

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

 in size," basing the opinion on the coefficient of variation 

 in the number of spines and the standard deviation in the 

 length of the tibia. In the former case the data certainly 

 do not permit a clear conclusion one way or the other, but 

 the value of the character which represents the sum of 

 the teeth of the sex combs of the right and left proximal 

 tarsal segment, where there is undoubtedly correlation, 

 may be open to objection under any consideration. If, 

 however, from the data presented in the study the value 

 of the coefficient of variation is computed, which, strange 

 to say, was not done in the paper, and thus allowance 

 made for the greater length of tibia in the cross-bred 

 forms, the combined inbred forms exhibit a variability 

 relatively 68 per cent greater than the cross-bred forms. 



Jennings (1911) in summarizing breeding experiments 

 with Parameciuvt concluded that "The progeny of con- 

 jugants are more variable in size and in certain other 

 respects than the progeny of the equivalent non-con- 

 jugants," and farther, "Thus conjugation increases varia- 

 tion." Continuing the investigations, he subsequently 

 stated (1913) that conjugation increased the variation in 

 the rate of reproduction. While the careful methods used 

 by Jennings have brought to light many interesting and 

 valuable facts, it is evident, from a critical consideration 

 of the data, that they by no means allow such conclusions. 



So far as size is concerned in a pure race, non-con- 

 jugants and their progeny were more variable than con- 

 jugants and their progeny, as noted in Table No. 28. In 

 a wild race the progeny of the conjugants were slightly 

 more variable than the progeny of the non-conjugants, as 



