Vol. 3] Kofoid. — Asymmetry in Triposolenia. 129 



of an org'anism with its antero-posterior axis in a horizontal posi- 

 tion is brought about by a turning of its body on this axis in the 

 direction of its left over to its right, and the leiotropic by turning 

 in the opposite direction, to wit, from its right over to its left. In 

 the Dinoflagellates generally the rotation is predominantly from 

 left over to right and structural differentiations which favor this 

 predominance in the direction of rotation are not infrequent, 

 such, for example, as the distal displacement of the girdle giving 

 to it the form of a descending right spiral. Such differentiations 

 usually result in some bilateral asymmetry. The only structural 

 character of this sort inTriposolenia appears to be the asymmetry 

 in the lists about the flagellar pore. 



As Jennings^ has clearly shown, this rotation upon the axis, 

 with resulting spiral course of greater or less radius, is a most 

 effective means of securing progression in a definite direction. 

 The radius of the spiral is largely influenced by the degree of 

 asymmetry of the organism, being greater as the asymmetry in- 

 creases. 



There is in Triposolenia, however, a form of bilateral asym- 

 metry which, though it may be coordinated with the spiral rota- 

 tion of the organism, is nevertheless also a most perfect adap- 

 tation to flotation in that it serves to orient the body during 

 passive descent in response to gravity, in the position of greatest 

 resistance. I refer to the distal deflection of the tips of the an- 

 tapical horns to the left. 



The principal necessity which confronts pelagic organisms is 

 that of keeping within range of the food supply, which for most 

 organisms means keeping within a certain distance of the surface 

 of the sea. In the case of Tnposolenia the organism is dependent 

 to some extent upon illumination for its synthetic processes. The 

 degree of light necessary is apparently not great since its center 

 of distribution appears to be nearer the hundred fathom line 

 than to the surface. The constant action of gravity tends to draw 

 the organisms below the levels of optimum illumination. It is 

 essential, then, to the welfare of the organism that its locomotor 

 activities should preserve its location in the region of optimum 



^ Jennings, H. S. : On the Significance of Spiral Swimming of Organ- 

 isms. Am. Nat., Vol. 3.5, pp. 369-378, 11 figs., 1901. 



