3 6 



HEFFERAN. 



[VOL. II. 



III. CORRELATION TABLE. 



degree of correlation between the right and left sides is, on 

 the whole, rather high. It seemed at first a somewhat unex- 

 pected result that the correlation in the variability of what I 

 have called the indefinite teeth should be higher than in that 

 of the definite teeth. If the correlation had been perfect it 

 would have meant that those causes which produced a devia- 

 tion from the mean in the left sets acted in the same degree 

 on the right sets also. Is it possible then that different causes 

 may have acted or that the same cause may have been effect- 

 ive in different degrees in producing the variability in the 

 definite and the indefinite teeth ? 



This question drew my attention more closely to a fact 

 noticed only incidentally in counting the teeth, i.e., in case of 

 animals having dark, heavy jaws, evidently older animals, the 

 definite teeth were fewer in number than in case of small, 

 young individuals. In the older jaws the teeth began farther 

 from the tip, leaving a smooth point, while the younger, more 



