No. 585] 



A STUDY OF ASYMMETRY 



537 



Bearing in mind always that the frequency between the 

 warm littoral and the cold abyssal temperatures is exag- 

 gerated because of the segrega- 

 tion in the warm littoral zone of 

 the most asymmetrical genera x 

 and species in many of the fam- ' \ 



ilios inhabiting intermediate tern- / \ 



peratures, it is clear that asym- / x < 



metry is least developed at the , \ 



optimum temperature for crinoid 

 life, and most developed in tem- 

 peratures which are phylogenet- 

 ically too warm or too cold. 



This agrees perfectly with what 

 we found from an examination of 

 the bathymetrical distribution of 

 asymmetry. 



A comparison between the fre- 

 quency of the families of crinoids 

 represented in the recent seas, 

 including only symmetrical spe- s ??SSSSS S SS S 

 cies, given in the actual numbers <o«££««£&5$»S 

 and also as percentages of the ferent Temperatu.es i ,1. 

 total numbers, and the frequency ficai^'s^^s"^^^^™^ 



Of the families including asym- those Including Symmetrical 



metrical species, given in the same Species onlJ ( } - 

 way, follows (Fig. 3) : 



