12 MEMOIRS OF THE UNIVERSITY OF CALIFORNIA 



addition of new organelles, and 1iy parasitism, with its resulting profound 

 modifications of the entire organism. 



In those organisms included in the old group Pyrocystidae (or P}Toeys- 

 taceae), which probably represent tx'jiical encysted phases in the life cycle of 

 certain genera of the dinofiagellates, the encysted stage or period has become 

 prolonged, while the free, motile g^^nnodinium-like stage is reduced to a rela- 

 tively short period (fig. I). It is in the free, motile stage, usually obscured in 

 the huge, inflated sphere of the encysted organism, that its relationships to other 

 dinoflagellates and the usual details of its specific organization must be looked 

 for. The details of the loss of flagella and their subsequent outgrowth in these 

 stages liave not been followed. In the ordinary encysted stage of the Gynmo- 

 diniidae both flagella are apparently absorbed at the beginning of encystment, 

 and towards the end of the period may be seen as very short outgrowths, indi- 

 cating a new formation for both flagella. The possibility of their being cast 

 off is not precluded. It is not unconmion to find encysted individuals with 

 neither longitudinal nor transverse flagella present. 



A still more profound modification has taken place in the little known group 

 of parasitic dinoflagellates. The free, motile stage, which is brief, and alone 

 shows the genetic relationships of the species, has the characteristic organiza- 

 tion of Gymnodiniiim, with the typical motor organelles (fig. J, 5). With the 

 beginning of a parasitic career these are lost and the organism liecomes a huge 

 non -motile, sacklike structure infesting the tissue of its host (fig. J, 1). 



In Protodinifer (fig. E, 2), Pavillardia (fig. JJ), Noctiluca, and most strik- 

 ingly in Erythropsis (pi. 12), the development of a tentacle or prod has resulted 

 in the loss or ahnost complete disappearance of the longitudinal flagellmn. An 

 occasional individual, with both flagella in addition to the prod in Eri/fhropsis, 

 as in E. ))ii)ior (pi. 12, fig. 131), confirms the suspicion that this condition is only 

 a secondary modification. In Noctiluca the transverse flagelkun also has been 

 reduced in size and lies in a short groove which soon fades out and is probably 

 the remnant of a girdle (fig. KK), though the inflation of the body makes its 

 exact status difficult to determine. 



The normal function of the prod of Erythropsis in the usual habitat of the 

 anunal is not made evident by the activities observed. Erythropsis is a ewpe- 

 lagic organism. It is a member of a group of dinoflagellates, none of which, ex- 

 cluding Amphidinium, so far as evidence at hand goes, ever has normally any 

 relation whatever to the si;bstrate. ]SIoreover, as far as oiu' limited observations 

 go, it could not compare with the usual flagellar equipment of the G,^annodi- 

 nioidae as an organ of propulsion in free-swimming movements. It might give 

 a spasmodic thrust to the body, but its presence, in E. e.rtrndens (pi. 12, fig. 

 130) especially, constitutes a serious impediment to locomotion, at least in the 

 extended state, since it considerably increases the resistance of the body to the 

 water, and, unless throwTi back into a trailing position, its as\iinnetry, with 

 respect to the main axis of rotation and progression, is fonnidable. 



