Vol. 3] Kofoid. — Asymmetry in Triposolenia. 133 



ing' manner which involves frequent returns to the horizontal 

 position. In the case of Triposolenia in suspension in the sea- 

 water, to whose specific g-ravity it closely approaches, the hori- 

 zontal position and the subsequent shiftings presumably occupy 

 a longer time than in the case of the model in the air. This is 

 easily demonstrated by sinking a model of firm hard paper in a 

 tall jar of water. 



Other genera than Triposolenia exhibit this type of asym- 

 metry. It is seen in a similar structural deflection in the allied 

 genus Amphisolenia in a large number of species, especially in 

 those of linear form. Linear species of Ceratium also have 

 marked deflection of the left antapical horn to the left and dor- 

 sally. This is noticeable in C. fusus Ehrbg. and C. stricticm 

 (Okannira). In species of Ceratium with anteriorly deflected 

 antapicals the two horns are sometimes deflected ventrally in a 

 sweeping curve. In Peridinium and Heterodinium the girdle is 

 often oblique antero-dorsally and ventro-posteriorly. These va- 

 rious types of asymmetry all have the tendency to orient the 

 passively sinking organism broadside to the direction of descent 

 and thus to increase the area of resistance. These forms of bilat- 

 eral or dorso-ventral asymmetry among the Dinoflagellates are 

 thus adaptative to flotation. 



Zoological Laboratory, University of California, 

 October 3, 1906. 



