KOFOID AND SWEZY: UNAKMORED DINOFLAGELLATA 231 



The nucleus is a large ellipsoidal body near the center of the organism. Its major and 

 minor axes are about 0.5 and 0.3 transdiameter in length respectively. 



The cytoplasm is clear and finely granular. No pusules have been observed. The color is 

 greenish yellow. These small forms have not been positively identified after leaving the cyst, 

 hence nothing can be said in regard to their nutrition and activities. Very many small indi- 

 viduals of this geniis have been observed in the material under examination, but the rapidity 

 of their movements has prevented a critical examination. 



Life Cycle. — Gymnodiniinn hoiiiJa is one of the very few members of this 

 group of which we have any detiuite knowledge of more than one stage of its 

 life cycle. 



Schiitt (1895-96) figured the crescent-shaped encysted forms and suggested 

 their connection with Pi/ roc// fit if; nndiluca ^Murray (1885), but it was not until 

 the publication of Dogiel's (1906) studies on this species that the connection 

 between these and the large globular forms, similar to or identical with P. 

 noctiluca, was established. 



Owing to a complete lack of knowledge of the development of the dinofla- 

 gellates. the discovery of these stages was given a greater importance than 

 facts later revealed warranted. As a result these species were isolated from 

 Gymnodinium and placed in a separate family of algae, Pyrocystiae, by Black- 

 man (1902). It has l)een pointed out elsewhere in this paper that indications 

 lead to the conclusion that these stages are normal ones in the life cycle of many 

 foiTus, including Gonj/anlax, Gymuodininm. and Gyrodinium, and that the 

 spheroidal or variously shaped, non-motile cysts probably are a part of the 

 developmental cycle of most of the dinoflagellates. Dogiel (1906) pointed out 

 the desirability of further investigation before separating Gymnodinium lunula 

 from the rest of the genus, and his conclusions are confirmed by later work. 



The life cycle, or the part thus far brought to light, may be divided into 

 three parts, the relative lengths of which are unknown. One of these is the 

 huge globular cyst, largely filled with vacuoles with the nucleus and most of 

 the cytoplasm localized at one side close to the periphery, from which proto- 

 plasmic strands extend out to the enclosing wall (fig. I, 1). This cell divides 

 into eight or sixteen moieties within the primary cyst and each of these parts 

 in turn becomes enclosed in slender crescentic secondary cysts (fig. I, 3, 4). 

 This process produces the second part or stage shown in plate 3, figure 55. The 

 contents of these cysts may divide into two or as many as eight moieties, each 

 of which develops a girdle, a sulcus, and the two flagella (fig. I, 7) and breaks 

 out of the cyst as a t^qjical Gymnodinium. During the third part of this cycle 

 the individual may divide, either in the motile condition or on encystment 

 (fig. I, 9-11 ). This may be repeated many times a]iparently bef(U-c any further 

 change takes place. What occurs between tliis stage and the production of tlie 

 large spherical primary cyst is as yet unknown. 



Dimensions. — Length, 22/^; transdiameter, 17m; axes of nucleus, 7m to 10m 

 and 5m to 7m; length of crescent-shaped cyst, 104m; diameter of large globular 

 cyst, 155m. 



