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MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



it is in the thecate forms. The daughter cells in Ceratium are attached to each 

 other at a definite point, the attachment area, which is the distal end of the 

 girdle of the anterior cell and the apex of the posterior cell (Kofoid, 1909f). 

 These jjoints form the last bridge of direct protoplasmic contimiity before final 

 separation of the dangiiter individuals. This relation of the two daughter cells 

 is identical in every respect with that which we find in Cochlodinium (fig. L, 4) . 

 The more plastic body of these naked forms allows greater freedom of move- 

 ment and mutual adjustment than in the thecate forms. The relative dorso- 

 ventral orientation of the two cells is frequently reversed in their struggle for 

 freedom and separation by the rotation of one of the two schizonts and twisting 

 of the protoplasmic strand attaching them to each other. 



Fig. M. Dividing Gymnodinium heterostriatum nom. sp. nov. After Dogiel (1906, pi. 2, figs. 54, 55). 1. 

 Late anaphase of division of the nucleus. Note oblique position of nucleus. 2. Daughter schizonts nearly 

 parted. The final separation takes place at the region of the distal ends of the girdles, as in figures L, 3, 4. 

 X 500. 



Further confirmation of oblique fission is found in Gymnodinium hetero- 

 striatum (fig. M) as portrayed by Dogiel (1906). Here the same relations of 

 structures are foimd as in Ceratium, with the final separation of the two 

 daughter cells occurring at the same place, namely, the anterior end of one and 

 the distal end of the girdle region of the other. As in Ceratium, too, the char- 

 acteristic features of the body become fully developed before final separation 

 of the two daughter individuals takes place. 



There is some evidence that division in Oxyrrhis is oblique (Keysselitz, 

 1908) and that the daughter cells occupy a position similar to that of Cochlo- 

 dinium citron at the close of mitosis but prior to plasmotomy. 



This condition is strikingly different from that obtaining in other groups 

 of the flagellates, where the separation begins at the anterior end and proceeds 

 to the opposite pole. This process in other flagellates never I'esults in chain 

 formation of the daughter cells, such as is the rule in the diuoflagellates (tig. L). 



