2 4 



C. C. Engberg 



From the fact that the posterior chord length follows more 

 closely the total length of the hook than does the anterior chord 

 length, we see that, as the hook gets larger, the increase is more 

 in the root than in the claw. This, it seems to me, has an impor- 

 tant hearing on the question of the functions of the hooks. The 

 fact that the firmness of the fastenings of the hooks increases 

 relatively faster than the length of the claw indicates that the 

 hook is intended for rough work, such as grasping — thus en- 

 abling the worm to attach itself to the walls of the intestines — 

 tearing and lacerating. 



We also see that characters c and d are very slightly corre- 

 lated, which means that the shape and size of the claw are nearly 

 independent of each other. 



MEAN, STANDARD DFVIATION, AND COEF. OF VARIABILITY 



These figures clearly disprove the assertions made by biologists 

 that character a is the most variable part of the hook. Its stan- 

 dard deviation is, to be sure, the largest of the standard devia- 

 tions, but its coefficient of variation, i. e., its relative variability, 



214 



