Vol. 3] Kofoid. — Asymmetry in Triposolenia. 131 



limit of optimum illumination, or even beyond possible photo- 

 synthesis. The return to the optimum levels can only be made 

 at some expense of energy. Any structural provision, therefore, 

 which loM^ers the rate of sinking will be of distinct advantage in 

 that it prolongs the stay at optimum levels, and reduces the ex- 

 penditure of energy in the return to such levels, when once grav- 

 ity gets the upper hand of the locomotor powers of the organism. 



Temporary cessations in the locomotor activities of Triposo- 

 lenia expose the organisms to the action of gravity and descent 

 begins while the organism is in a vertical position, with the mini- 

 mum form resistance to the downward movement. 



It is obvious that if the organism should turn so that it should 

 lie on the side the area of displacement would be greatly in- 

 creased and the descent delayed. This is accomplished by the 

 terminal asymmetry of the antapical horns in Triposolenia. As 

 has been indicated in the description of the species in the previous 

 paper, the ends of the antapicals are bent to the left for a short 

 distance in all species which have been examined on this point. 

 The effect of this asynuuetry is to turn the organism upon its 

 right face, as soon as it begins to descend while oriented with 

 the anterior end uppermost. The greater resistance offered by 

 the right face of the tips veers the antapices to the left and throws 

 the organism over on its right side, as shown in Fig. B. This may 

 be beautifully demonstrated by dropping in the air a paper model 

 of Triposolenia in which the antapicals are slightly bent. The 

 turning of the model, made from a drawing showing an enlarge- 

 ment of 675 diameters, is accomplished easily within a meter of 

 descent, and often in less than that distance, that is, within ten 

 lengths of the organism. The rapidity and despatch with which 

 the model turns is remarkable and is significant of the effective- 

 ness of this structure in changing the orientation of the organism 

 when sinking' with a vertical orientation. 



The deflecting effect of the bent ends of the antapicals nat- 

 urally decreases as the organism turns upon its side, since they 

 include a rapidly decreasing proportion of the total surface of 

 resistance. When once turned upon the side the horizontal or- 

 ientation of the model continues for a short time and the descent 

 proceeds with frequent changes of position in a fluttering, waver- 



