Schultz 1933) it was possible to divide the combined sample of 40 into 

 separate male and female subsamples of 23 and 17, respectively. Since 

 such data are clearly more valuable than those for combined-sex samples, 

 the newly computed data for male and female siamangs separately are 

 included in Tables 4, 9, and 12. These show that the capacities for 23 

 male siamangs are symmetrically distributed, whereas those for the smaller 

 sample of 17 female siamangs are slightly positively skewed. 



To summarize on the hylobatines, for male and female H. lar the 

 differences between the deviations of the smallest and largest values for 

 each sample are 0.79 S.D.s and 0.49 S.D.s, respectively, while for the small 

 samples of H. agilis (combined sexes) and male and female siamangs 

 the corresponding differences are 0.33 S.D.s, 0.12 S.D.s, and 0.87 S.D.s, 

 respectively. If we regard values of less than 0.40 as representing sym- 

 metry, values between 0.41 and 1.00 as indicating slight skewness, and 

 values of over 1.00 as showing definite skewness, all of these hylobatine 

 values may be considered small enough to permit the distribution curves 

 to be regarded as virtually symmetrical or, at most, only slightly skewed. 



In the chimpanzee sample the maximum and minimum values for 

 pooled one-sex samples are close to 3 standard deviations above and below 

 the mean, respectively (Table 12). The neglible difference between the 

 deviations of the 2 extreme values is —0.13 S.D.s for males and —0.01 

 S.D.s for females. 



For orangutan capacities, the male distribution curve is very slightly 

 skewed to the left. The highest value (540 c.c.) is 2.64 S.D.s above the 

 sample mean, whilst the lowest value (320 c.c.) is 2.87 S.D.s below the 

 mean. The difference between the deviations of the 2 extreme values 

 in the sample is —0.23 S.D.s. On the other hand, the female orang 

 sample is slightly positively skewed, the difference of the extreme devia- 

 tions being +0.54 S.D.s. However, these asymmetries are again slight 

 and compare well with the values for hylobatines. The overall effect 

 is of symmetrically distributed samples of orangutan capacities. It is 

 interesting to note, however, that Vallois's combined-sex sample of 260 

 capacities is definitely negatively skewed, the highest value being only 

 2.01 S.D.s above the sample mean, whereas the lowest value is no less 

 than 3.66 S.D.s below the mean. I drew attention to this apparently 

 exceptional distribution in a previous publication (Tobias 1968b). No 

 fewer than 2 of the orang subsamples, Selenka's males and Oppenheim's 

 females, show slight negative skewing, 5 are more or less symmetrical, 



& 56 



