KOFOID AND SWEZY: UNAKMOKED DINOFLAGELLATA 25 



observed it in four species of Pouchctia, P. juno, P. rosea, P. fusus, and P. 

 conipaeta, and also iu two species of Erijfhropsis, E. cochlea and E. cornnta, 

 though these two species he placed in the genus Pouchetia. Noting the advanced 

 degree of development of this pecidiar structure, he formed the genus Pouchetia 

 for the oeellate dinoflagellates and placed therein all of the ocellate species 

 described earlier by Pouchet. 



Schiitt distinguished two types of ocelli, one with ])rownisli black pigment, 

 as in P. scliHctti (P. rosea Schiitt), the other with reddish black pigment, as 

 in P. fusus. The relation of these two colors, red and brown or black, in a 

 single pigment mass he did not observe. The lens he described as composed of 

 a single part, as in P. cochlea, or of several smaller moieties, as in P. scliuetti. 



Hertwig (1884) gave a fairly accurate account of the eyespot in Erijfhropsis 

 agiJis, describing its component parts as lens and pigment mass. Faure-Fremiet 

 in 1914 gave a fuller account of the structure of this organelle in the genus 

 Erythropsis than had yet been attempted for any of the ocellate dinoflagellates. 



The various points in which these descriptions differ from our own will be 

 noted as we continue our discussion of this structure. 



The ocellus of the Pouchetiidae is composed of two distinct parts, a refrac- 

 tive, hyaline, sometimes spherical lens (fig. PR, 1), and a surrounding pigment 

 mass or melanosome (fig. PR, niel.). The lens or cristalline body of Pouchet 

 varies in shape in the different species. In its more highly integrated form it 

 is usually spheroidal in shape, clear and colorless and often asymmetrically 

 laminated. This stage is reached in many of the species of the genus Enjth ropsis 

 (pi. 12, figs. 129, 133), as well as in a few species of Pouchetia (pi. 11, fig. 118). 

 In some cases, where distinct lamellae are not seen, its optical properties produce 

 a play of colors not unlike that of a soap bul)ble (pi. 10, figs. 131, 134). In 

 other species the shape may vary to an elongate form, more or less irregular in 

 outline (pi. 6, fig. 61; pi. 11, fig."l26). 



On c;^i;olysis of the body the lens persists and when foimd free in the water 

 it presents a colorless appearance. In the living organism it often reflects 

 some tints of the surrounding c;si;oplasm (pi. 8, fig. 87) when partly buried 

 within it. or it may show only a few of the prismatic colors when its position is 

 protuberant above the cytoplasm, as in Erythropsis pavillardi and E. cornuta 

 (pi. 12, figs. 133, 129). 



The size and shape of the lens is not always easy to determine, since it is 

 more or less covered l)y the melanosome. A certain amount of correlation be- 

 tween the size of the organism and the size of its ocellus is found in nearly all 

 the members of the group. Pouchetia parva, one of the smallest species in the 

 Pouchetiidae, has a length of 31/^ for the body and a diameter of about 7m for 

 its ocellus. This is the smallest lens found in any species. The ratio between 

 the size of the bod,v and of the lens is greater here, however, than the ratio found 

 in any other species. Thus in Erythropsis cornuta (fig. SS, 1) the lens has a 

 diameter of 22^* \vhile the body has a length of IOIik In the largest species of 



