W. E. ALKINS — Morphogenesis of Brachiopoda 

 TABLE II. 



Comparison of Depth with Length. 



The solid figures show that Reticularia lineata presents a very 

 good example of a truly homogeneous species: the variation 

 shown is perfectly continuous throughout, and there is not the 

 slightest evidence of any tendency towards a differentiation into 

 two or more groups. Such solid figures may be taken as typical 

 of " good," simple, homogeneous species. 



Ontogeny. We may now safely proceed with a mathematical 

 investigation into the ontogeny of the shell. 



From the data necessary for the construction of the length- 

 width and length-depth distribution figures the mean value of 

 the width and depth respectively corresponding to each length 

 was calculated. These mean figures are included in Tables I 

 and II. They represent the average width and depth of shells 



