KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 



69 



An endoparasitic mode of life places the heaviest burden upon the developing 

 organism, resulting in greater modifications of the ))ody, usually in larger size 

 and in a more complicated type of development than is generally characteristic 

 of the ectoparasitic or non-parasitic forms. Whether these dinoflagellates are 

 facultative or obligatory parasites is a question, as their further development is 

 entirely unknown. 



Binary and Multiple Fission. — Binary fission in the Cxymnodinioidae has 

 been noted by many investigators, but critical observation on the details of the 

 process has been lacking. This process has been followed out in the thecate 

 forms by Lauterborn (1895), Borgert (1910), and Jollos (1910), among others. 

 It differs from that found in the typical flagellate in that the plane of division 



Fig. L. Binary fission in dinoflagellates. 1 and 2. Ventral views of dividing Ceratium hirundinella (O. F. 

 M.). After Lauterborn (1895, pi. 13, figs. 1.3, 14). X ? 1. Division of cytoplasm nearly completed, theca 

 parting along sutures (marked by heavy lines). 2. New thecal plates beginning to form. 3. Ventral view of 

 Ceratium in chain. After Kofoid (1909, pi. 1, fig. 1, two anterior schizonts and apical horn of the third). 

 X 405. 4. Daughter schizonts of Cochlodinium citron Kofoid and Swezy. After Kofoid and Swezy (1917, 

 fig. 8). X 937. 



is oblique and not longitudinal as in the larger group. In the thecate forms 

 this is undoul)tedly an adaptation made necessary by the peculiar arrangement 

 of the plates, and enal)les the two moieties to separate at the sutures (figs. L, 

 1, 2) and not by the division of single plates, as would othermse be necessary. 

 The plane of division of the simpler Gjannodinioidae appears to be more 

 nearly longitudinal, like that of the t}q)icai flagellates. In Prorocentrum the 

 l)ivalve theca parts along the longitudinal suture. However, in division in the 

 more specialized Gymnodiuiidae, as in Cochlodinium, the position of the two 

 daughter cells strikingly resembles that in Ceratium (figs. L, 3, 4) at division 

 and leads to the conclusion that division in the unarmored forms is oblique as 



