KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 57 



these will suffice to show that France 's work cannot be accepted without further 

 investigation and confirmation on this point. 



The stigma of the fresh-water dinoflagellates, as in Glenodininm cincfmn, 

 Gymnodinmm pnradoxum, and Gyrodinium hi/aUnum, is likewise a simple \\n- 

 differentiated mass of granular pigment, located in the A^entral suleal area, near 

 the origin of the longitudinal flagellum. These structures seem to be homol- 

 ogous with the stigmata of the flagellates, apparently identical in sti'ucture and 

 probably in origin. The widespread occurrence of this organelle throughout 

 the fresh-water Flagellata woidd suggest a correlation between its development 

 and its environment, since it is rarely if ever present in the marine forms. 



On the other hand, the entire absence of a stigma of this type in the simpler 

 dinoflagellates of oceanic waters would suggest the improba])ility of its forming 

 one of the developmental stages of an organelle which is found only in the 

 highly specialized pelagic species of the Pouchetiidae. No adequate evidence 

 is forthcoming to show the presence of intermediate stages between these two 

 types of structures. 



These facts then jioint towards the conclusion that the ocelli of the dino- 

 flagellates is not a derivative of the stigma commonly present in the fresh-water 

 species of this group, as well as in other flagellates. Evidence seems also to 

 point to a connection between scattered pigment occurring in many of the 

 marine species and the progressive formation of the melanosome of the Pouche- 

 tiidae. We have, therefore, confined the term stigma to the simple mass of 

 pigment granules present in the lower forms, and use the term ocellus for the 

 more highly specialized organelles of the Pouchetiidae. 



In its structural efficiency, as found in Eri/thropsis, it is probably fully equal 

 to the ocelli found in the medusae of the Hydrozoa, which may consist of a 

 cluster of pigmented cells or a cup of pigmented cells filled with a spherical 

 thickening of the cuticle to form a lens. The difference is here mainly one of 

 size, that of the medusa having several cells uniting to perform a function 

 which in Eryth ropsis is confined to parts of a single cell. The minute structure 

 of the lens and its exact relations to the melanosome have not been investigated 

 in the Pouchetiidae, beyond observations on the living organism. When this 

 has been done it may reveal structural similarities which will indicate more 

 clearly its relationships than can be shown with our present knowledge of this 

 organelle. That it is a light-receiving organ and a fairly efficient one the details 

 of its structure would indicate. 



PusuLES. — The cytostomal area of the dinoflagellates is represented in the 

 sulcus and the flagellar pores on the ventral surface, its internal extensions 

 taking the form of pusules. The reasons for these conclusions have been pointed 

 out elsewhere. The fundamental underlying oi-ganization is directly compar- 

 able with that of similar structures elsewhere in the Protozoa, and consists 

 essentially of a groove in the surface leading to the opening through the plasma. 

 Each group of Protozoa in which this structure is found has its own peculiar 



