BLASTOGENIC VARIATIONS. 179 



Now it has already been found, in the case of stature in 

 man, that the correlation between mid-parent (i. e., 

 mean between male and transmuted female) and off- 

 spring is .424, and the regression of offspring on mid- 

 parents .6;* hence Warren's values seem to show that 

 the parthenogenetic mother acts as a mid-parent to her 

 offspring, and not as a single parent, and also that these 

 offspring exhibit regression towards the mean race type, 

 just as sexually produced individuals do. As Warren 

 himself points out, however, his evidence is not con- 

 clusive. Thus the number of individuals measured 

 was comparatively small, and also it would seem that 

 Daphnia is a very unreliable organism to work with. 

 It is so exceedingly sensitive to its environmental con- 

 ditions f very considerable variations being produced 

 by comparatively slight changes that these data de- 

 rived from it can only be accepted with considerable 

 reserve. 



A further series of observations was made by War- 

 ren J upon Aphides (Hyalopterus irirhodus). Sixty 

 parents and their 368 children were measured, and also 

 30 grandparents and their 291 grandchildren. War- 

 ren found that the coefficients of parental and grand- 



* It has been stated in the previous chapter that the coefficients of 

 correlation and of regression between single parent and offspring are 

 practically the same thing, and are equal to .3. The coefficient 

 of correlation between mid-parent and offspring is, however, 

 /y/2 x .3 = .424, because the mid-parent, being the mean of two 

 parents, is less variable than the single parents (in the proportion of 



1 to -/o). The coefficient of regression of offspring on mid-parents, 



is, however, twice that of offspring on a single parent, i. e., is .6. 

 \Vide Q. J. Microsc. Sci., vol. xliii. p. 199, 1900. 

 t Biometrika, i. p. 129, 1902. 



