water above and below the optimum, and least at and just 

 below the optimum temperature. 



Considering only the genera marked with an asterisk 

 (*), that is, the genera with the most highly developed 

 asymmetry, we find the same general facts emphasized as 

 in the case of all the genera including asymmetrical 

 forms ; but here the minimum is between 50 and 400 fath- 

 oms instead of between 100 and 650 fathoms. The tem- 

 perature at 400 fathoms is 41.8°. This approximation of 

 the minimum to the zone of optimum temperature when 

 only the most asymmetrical types are considered 

 strengthens the hypothesis that the zone of optimum 

 temperature really represents the zone of least-developed 

 asymmetry. 



