UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 18, No. 6, pp. 89-102, 12 figures in text December 14, 1917 



ON THE ORIENTATION OF EBYTHROPSIS 



BY 



CHARLES ATWOOD KOFOID and OLIVE SWEZY 



(Contribution from the Zoological Laboratory and the Scripps Institution of Biological Research of the 



University of California) 



The dominating factors in the morphology of the Dinoflagellata 

 and in their evolution as a group are the two flagella. The location of 

 their points of origin upon the surface of the body determines the 

 ventral surface. The course of the transverse flagellum which pur- 

 sues a spiral direction in the girdle about the body delimits the epicone 

 and hypoeone in the Gymnodinioidae and in the thecate forms sepa- 

 rates the epitheca from the hypotheca. The plates of the theca form 

 zones above and below this girdle. The proportions of the body are 

 profoundly influenced by the direction (ascending or descending), and 

 steepness of the spiral and the amount of torsion of the body which has 

 been developed in the direction of the stress which the activity of this 

 powerful flagellum creates in the girdle. 



The transverse flagellum lies in a depression or girdle which has 

 one general direction on the body of the dinoflagellate, namely, that 

 of a spiral from its point of origin at the anterior flagellar pore at 

 the anterior junction of the girdle with the sulcus on the midventral 

 face, transversely across the left side, thence across the dorsal surface 

 and around upon the ventral face to the reunion of the girdle with the 

 sulcus. If this reunion at its distal end is posterior to the origin the 

 spiral is a descending left one. If it is anterior to the flagellar pore 

 the girdle forms an ascending left spiral. If there is no anterior or 

 posterior displacement the girdle forms a circle instead of a spiral, a 

 condition rarely realized. The direction here described from the ven- 

 tral face to the left of the body and over dorsally to the right, is 

 universal in dinoflagellates above the Prorocentridae. 



There are, in literature, seeming exceptions to this generalization. 



'o. 



> DEC 28 1917 <i' 



