60 A. FRANKLIN SHULL 



affect the, result. The standard deviation of the duration of the 

 egg stage is 7.79, less than in D X D, but considerably greater 

 than in C X C or C X D. The hatching has been spread over 

 a considerable time, but not so great a time, relative to the 

 number hatching, as in D X D. 



Some correction in the standard deviation of the duration of 

 the egg stage seems netessar^-. If the eggs be collected over a 

 long period, and all be .put into one lot for records of hatch- 

 ing, it is obvious that the hatching will be spread over a cor- 

 respondingly longer period, and the standard deviation thereby 

 increased. Since the four lots of eggs to be compared (C X C, 

 C X D, D X C and D X D) were not obtained in the same 

 length of time, the apparent variability of the duration of the 

 egg stage is not the true variability. To correct this error in 

 some measure, I have computed the standard deviation of the 

 laying of the eggs, and deducted it from the standard deviation 

 of the hatching. Some computation was necessary to determine 

 when the eggs were laid; but as the number of females mated in 

 one day, and the number of eggs laid by each, is known, and as 

 the fertilized eggs of one female are laid over a period of about 

 five days, a fair approximation of the time of laying may be 

 had. After this adjustment, ttie standard deviation was com- 

 puted, and is given at the bottom of each of the four tables 

 of hatching (indicated by ctl ; o-^ indicates the standard deviation 

 of hatching). It is believed that deducting a^ from a-^ is a 

 sufficiently accurate correction within the limits in which it is 

 used. 



If, now, the four lots to be compared are arranged in a series, 

 as in figure 1, with the inbred eggs {C X C and D X D) at the 

 ends, and the reciprocal crosses between them, each one near- 

 est the line that furnished the female parent, some interesting 

 facts appear. The standard deviations of hatching of the four 

 lots are 2.83, 3.44, 7.79 and 10.78, respectively; or, if we deduct 

 from each the standard deviation of laying, they are 1.09, 1.87, 

 5.64 and 7.14. From left to right, these four lots of eggs form 

 a series of increasing variability of the duration of the egg stage. 

 The most important feature is that the reciprocal crosses are 



