KOFOID AND SWEZY: UNARMOKED DINOFLAGELLATA 27 



rounds up into one or more spheroidal masses and undergoes the same fate. 

 In one individual of Eri/thropfiis c.rtntdeus o})served the complete disappear- 

 ance of the ocellus required twenty minutes from the tmie eytolysis began, the 

 lens being the last part of the structm*e to dissolve. 



Faure-Fremiet (1914) has found that under the action of dilute acetic acid 

 the pigment of the melauosomc is transformed into a nuiltitude of small globules 

 of which part are brown and part are red. He evidently did not observe the 

 red central core of the melanosome so prominent in some of our own forms 

 (pi. 12, figs. 131, 134), though less noticeable in others (pi. 12, figs. 127, 129). 

 The action of the acetic acid on the red pigment of the core explains the 

 presence of the red granules in his figure of the melanosome thiis treated. 

 Schiitt (1895) also failed to differentiate these two parts of the melanosome. 



Various stages of integration of the ocellus are found within the group. 

 The simplest form of the lens presented is that of separate, loosely aggregated, 

 hyaline spheres, with scattered pigment granules partly surrounding them 

 (pi. 11, fig. 125). From this simple condition a process of integration is clearly 

 evident within the ocellate group, whereby the scattered pigment spherules are 

 combined into a compact mass closely envelo])ing the base of the lens, with a 

 correlated combination of separate spheres into a single, spheroidal lens, the 

 greatest development of which is perhaps that of Erijthro}>sif! coruufa (pi. 12, 

 fig. 129), or E. paviUanIi (pi. 12, fig. 133). Various stages of this process 

 may be seen in the Pouchetiidae, beginning probably with the genus Prof apsis 

 (fig. LL) , though phases of the diffuse, less integrated types may also be found 

 in Pouchetia (fig. PP, 4). In Protopsis neapolitana (fig. LL, 2) the mela- 

 nosome is composed of relatively few pigment granules Avith a large' spheroidal 

 lens. A simpler condition is found in P. nigra (fig. LL, 1), where the lens also 

 presents the diffuse type, being composed of several small spheroidal bodies. 



In Nematodiiiinw jxirtifidn the ocellus is diffuse in structure (fig. NN, 4), 

 while in N. torpedo (fig. NN, 3) and iV. armation (fig. NN, 1) it presents a 

 progressive integration lioth in the lens and in the melanosome. 



Ocelli of the ditfuse tyi;)e are found in Pouchetia poucheti (fig. PP, 4) and 

 P. maxima (fig. 00, 2), while most of the other species of that genus present 

 a more or less well integrated type of structure. The extreme development of 

 the amoeboid character of the melanosome is found in P. suhnigra (fig. 00, 6) 

 and in P. alba (fig. PP, 8), where diffuse strands of lilack pigment wander out 

 through the cytoplasm. It is probable that the melanosome throughout the 

 entire group possesses tliis characteristic property of amoeboid movement in 

 varying degrees, as does the pigment found genei-ally in the G^^nnodinloidae. 



The position of the ocellus is such as to receive the stimulus of ligiit as the 

 animal rotates in forward locomotion. It seems to be fairly constant in most 

 of the members of the Pouchetiidae in its relation to the girdle and sulcus. 

 In the genera Protopsis, Neniatodinium, and Pouchetia it is usually found in 

 the posterior half of the body, at the left of the intercingular sulcus and anterior 



