GROWTH AND MORPHOLOGICAL CHARACTERS. 75 



for, the more pointed a skull is, the greater will be the quotient, pro- 

 vided the distance between these two transverse measurements remains 

 the same. The sagittal length of the skull between measurements 9 

 and 11 is in reality the altitude of a trapezoid, of which these widths 

 are the bases. There are two ways of dealing with the pointedness 

 of these skulls. One can take the ratio of the averages of measure- 

 ments 9 and 11, given in tables 63 and 64, or, one can take the average 

 of the ratios of measurement 9 to 11 in the individual skulls. Ratios 

 of averages and the average of ratios are not necessarily the same, to 

 be sure. The first case would mean the pointedness of an average or 

 ideal skull in a given class, and the second case would mean the average 

 pointedness of an arra}'' of many skulls in this class. Both sets of 

 quotients were calculated and are given in table 71. They are practi- 

 cally the same, and this is probably due to the high degree of corre- 

 lation between measurements 9 and 11 in any given class. 

 The indications are that: 



(1) The wild was more pointed than the tame. 



(2) The I wild were an apparent blend. 



(3) The I wild, according to the table, were the same as the ^ wild; 

 but as a matter of fact they were less pointed. The ^ wild skulls were 

 very large, and since the distance between the two widths (the altitude 

 of a trapezoid) was longer, the same ratio must mean that the | wild 

 were more pointed than the | wild. 



(4) The I wild were approaching the guinea-pig-skull shape. 



The coefficients of variability for the ratios of measurement 9 to 11 

 were calculated; but like the coefficients of variability for the linear 

 dimensions, they were small and showed no significant differences. 

 However, there is no doubt but that individuals were obtained in the 

 F2 and F3 generations which were identical with guinea-pigs. Possibly 

 we are justified in regarding these as segregates, due to the recombina- 

 tions of factors. 



EFFECT OF STERILITY IN THE MALES. 



Throughout the discussion the sterility of the males has been 

 neglected. In the case of non-functioning testicles it has been shown 

 that ossification is delayed, particularly in the long bones. Recently 

 Geddes (1910) has shown this to be the case in pathological conditions 

 as well as in castration. The measurements of all hybrid males in 

 table 63 were taken from fully sterile animals (except two males). 

 By sterile we mean that they lacked motile spermatozoa and were 

 incapable of fertilizing an egg. In many cases they showed no sperma- 

 tozoa at all in the epididymis. The averages and variability of these 

 sterile | wild males are so close to the guinea-pig that it may be safely 

 concluded there was no effect from such sterility. The number (60) 

 of instances is large enough to make the average significant. That 



