34 



SIZE INHERITANCE IN RABBITS. 



COEFFICIENTS OF SIZE. 



In order to get a clearer view of the variabilities treated in table 4 

 and to study variability by comparing whole animals instead of their 

 parts, it seemed desirable to find a coefficient for each individual that 

 would express the average of the sizes, or of the deviations of its dif- 

 ferent parts. As the measurements range from 2 to 10 cm., no absolute 

 average of deviations could be used, for a small deviation in a short 

 measurement would have far greater significance than an equal devia- 

 tion in a long measurement and so, in any average, the large deviations 

 in a long measurement would entirely overbalance the equally impor- 

 tant small deviations in short measurements. 



The following method based on relative deviations was employed to 

 obtain coefficients of size (C. S.) for each animal. The average of a 

 character for one fraternity was used as a dividend into which were 

 divided the individual measurements of the animals in the same fra- 

 ternity. The quotients so found gave a series of ratios expressing the 

 relative sizes of the various sibs above or below their mean. An animal 

 with a character at the mean would have a ratio of 1 for that character; 

 an animal whose measurement was shorter than the mean would have 

 a ratio above 1 ; an animal with a measurement above the mean would 

 have a ratio below 1. By this method the ratios of all the characters of 

 one animal to the corresponding fraternal means were obtained. The 

 average of these ratios gave the coefficient of size (C. S.) for that animal. 



In order to avoid giving too much importance to one dimension of the 

 skeleton and to escape errors occasioned by using characters unequally 

 subject to errors in observation, not all measurements were included in 

 calculating these coefficients of size. The second and third measurements 

 on the skull, P. O. and P. M., being functions of the total skull length, 

 were not used. The width of the palatine bridge (P.) was too small to 

 show any easily determinable variation. Only one zygomatic width was 

 included (Za.). The widths of the skull at the teeth (Te.), the brain 

 case (Be.), and the ears (E.) are generally very similar. 

 As the width of the brain case in animals with very long 

 skulls is often less than that of intermediate skulls, and 

 as the measurement at the ears is liable to larger errors 

 in observation than the width of the teeth, this last char- 

 acter (Te.) alone was used. The anterior height of the 

 skull (N.) is a short measurement and is as much influ- 

 enced by the degree of convexity of the nasal bones as 

 by any variation in bone size. The length of the nasal 

 bone being limited at one end by an extremely irregular 

 dentate suture is unsatisfactory in spite of its length. 

 Lists of the characters used and those not used in determining coeffi- 

 cients of size are given herewith. 



