No. 599] SHORTER ARTICLES AND DISCUSSION 



(597 



Mean 12.4365 ± .0182 11.9077 ± J 



Standard Deviation 1.4800 ± .0128 1.2803 ± J 



Coefficient of Variation 11.901 ± .105 10.752 ± J 



Thus instead of the females being "over 14 per cent, more 

 variable than the males" they are in absolute terms actually 

 .1997 ± .0175, or over 13 per cent., less variable. Relative vari- 

 ability as measured by the coefficient of variation is 1.149 ± .142 

 per cent, lower in the female that it is in the male. This lower 

 variability of the female is also quite in evidence if the ma- 

 terials be split up into groups with regular and irregular ar- 

 rangement of the nipples. Thus : 



For "Eegtjlar" Class 



= 1.485 ± .017, C. V. = 12.03 ± .14 



= 1.315 ± .021, C. V. = 11.16 ± .13 



0.170 ± .027, " 0.87 ± .19 



Ma 'es a — 1.461 ± .020, C. V. == 11.61 ± .16 



Females a== 1.210 ± .016, C. V. = 10.02 ± .14 



Difference 0.251 ± .026, 1.59 ± .21 



However measured, the variability of the number of nipples in 

 the female is always significantly less, not greater, than in the 

 male. 



Furthermore a rather noteworthy sexual differentiation seems 

 so far to have escaped notice. The mean number of nipples for 

 male pigs is in all cases higher than that for female pigs. Thus : 



11.9077 ± .1 



maies 12.3425 ± .0233 Males 12.5833 ± .0234 



Fema,es 11.7849 ± .0214 Females 12.0777 ± .0232 



Difference .... 0.5576 ±".0316 Difference "0.5056 ± .0330 



In all cases the males have on the average more nipples than 

 the females. The regularity of the differentiation is brought out 



