THE AMEBIC AN NATURALIST [Vol. XLIX 



hand to be larger than the left, and the left leg and foot to 

 be larger than the right. 



It is clear, therefore, that in dealing with asymmetry in 

 any group we must work inward from the most asymmet- 

 rical types toward the least asymmetrical, arbitrarily 

 erecting a barrier between what we call asymmetry and 

 what we are pleased to consider as "symmetry" at any 

 point we choose. 



Asymmetry — that is to say the maximum departure 

 from perfect bilateral or radial symmetry — appears to 

 follow certain definite lines wherever it appears, quite 

 regardless of the type of animal, or the form, in which 

 it is manifested. 



In the following pages we shall consider the wider 

 variations from t1:e typical pentamerous symmetry among 

 the recent crinoids, which is phylogenetically most exten- 

 sively developed at the consummation of the phylogenetic 

 lines, and physico-economically most extensively devel- 

 oped in the situations most unsuited to crinoidal exist- 

 ence, particularly in the very warm water of the East 

 Indian and north Australian littoral, and the very cold 

 water of the Antarctic regions and the deep abysses of the 

 oceans, and is least evident among phylogenetically con- 

 servative types, and in the situations which appear to be 

 best suited for crinoid life. 



As an indication of the possible fundnmental impor- 

 tance of the light thrown on the study of asymmetry by an 

 examination of the data offered by the recent crinoids, it 

 may be noticed and borne in mind that among the mam- 

 mals the phylogenetically aberrant asymmetrical narwhal 

 (Mouodon) is exclusively arctic; the phylogenetically 

 aberrant asymmetrical whales occupy a habitat very aber- 

 rant for the class; and the anthropoid apes, which are 

 pronouncedly right or left handed, live in very warm 

 regions; that among the birds the curious crook-billed 

 plover (Anarhi/nrhus), with the beak twisted to the right 

 and one side of the body lighter in color than the other, 

 occurs only in New Zealand, the home of many phyloge- 



