KOFOID AND SWEZY: UNAKMORED DINOFLAGELLATA 91 



La Jolla, as elsewhere, is fully exposed to the light and that the illmnination 

 in this latitude (33°) is fairly direct during midsummer. 



In the pelagic and neritic forms a wider range of variation in form is found, 

 combined with a generally larger size and more brilliant coloration. The f resh- 

 and brackish-water species are closely akin to the sand beach forms in their 

 general characteristics. They usually possess green or yellow ochre chromato- 

 phores, and are small in size, with a strong tendenc.y towards a dorsoventral 

 flattening of the body. These tendencies are shown in Amphidinium lacustre 

 (fig. U, 15), Gymnodinium tenuissimum (fig. AA, 7), and Gyrodinium hyalinum 

 (fig. CC, 15). 



Nutrition and Evolution.- — West (1916) has suggested that saprophytic 

 dinoflagellates are probably mostly degenerate forms. There is no evidence 

 for this, however. On the contrary, it seems cpiite probable that a saprophytic 

 mode of nutrition is a natural one for many of the Flagellata, and, furthermore, 

 that it is the intermediate stage between the holox:>hytic and holozoic tj'pes. 

 There are several reasons which point to this conclusion. One of these is found 

 in the intunate correlation existing between the method of food-getting and 

 the structure of the body. 



There is in many, if not most, of the holophytic flagellates a close correlation 

 between the presence of chromatophores and a thickened cuticle, or periplast, 

 surrounding the body. This is shown most strikingh' in Euglena. With the 

 disappearance of chromatophores the periplast becomes thinner, often scarcely 

 detectable as such, and remains so until a definite oral region has become evolved 

 with accessory structures for the ingestion of food. When this stage in the 

 evolution of the protozoan has been reached a corresponding amount of ecto- 

 plasmic differentiation takes place, most noticeable in the ciliates with their 

 more complicated structures. A secondary modification is found in the 

 Rhizopoda in the development of pseudopodia, correlated with a thin periplast 

 for the ingestion of food. Very many of the small flagellates which live in 

 stagnant water rich in decaying j^lankton show an absence both of chromato- 

 phores and distinct food bodies in the cytoplasm, as well as an absence of a 

 definitely marked cuticle. So far as evidence goes in these forms nutrition is 

 evidently of the saprophytic tj^pe. 



In the typical vegetable organism the raw materials enter the protoplast 

 in a state of solution and are there elaborated into assimilable form hy means 

 of special organelles and enzymes. This is a more primitive type of feeding 

 than the holozoic method, by which solid food substances are ingested. The 

 transition between the two methods must have been a stage in which the already 

 ela])orated material entered the protoplast ])y osmosis in a state of solution and 

 was ready for assimilation by the cell without the aid of special organelles or 

 enzjanes. A thin periplast covering the body is a very necessary factor in 

 feeding by osmosis, and we find this cell covering in its most ideal state among 

 these flagellates. A further advance in evolution is required before the organism 



