Ko. 490] ORTHOGENETIC VARIATION 



613 



shoulder and body, and approximately an angle of 45° between 

 the shoulder and the axis of coiling. From this the progressive 

 change is to a steeper shoulder in one series and to a flatter shoulder 

 in the other. Similarly, the partial embrace of the whorls seems 

 to be the norm, from which variation on one hand is in the direction 

 of more pronounced embracing, carried to excess in phylogerontic 



types, and in the other to a gnukial loss of power to cf)il, which 



may be represented in tlic foUowino- nuuuicr (Diaunim 1 i. 



The ambitus of the wliorl. or the point of i^vvnWM convexity, 



