KOFOID AND SWEZY: UNARMORED DINOFLAGELLATA 497 



The nucleus is a verj' clear, broadly ellipsoidal body in the anterodorsal region, with major 

 and minor axes of 0.5 and 0.4 trausdiameter respectively. It has an outer clear zone enclosed 

 within the outer nuclear membrane. No chromatin strands could be detected in its substance. 

 The cytoplasm of the body as a whole was throughout of a glassy, glaucous, hyaline appearance 

 with remarkably few alveoli or granules of appreciable size. 



The surface of the body is devoid of striae or other markings except for the lines and zones 

 paralleling the girdle. However, as the animal grows less active, peripheral vacuoles arrange 

 themselves in the subsurface zone in a somewhat linear fashion, with their longer axes longi- 

 tudinal and their lines longitudinally disposed, indicating at least an internal linear organization 

 of the peripheral layer of cytoplasm. 



DiMEXSioxs. — Length of body, 90-117/^; of extended tentacle, including 

 stylet, 60-70/^; of stylet, 17/*; diameters, transverse 70-85/', dorsoventral 7:>. 



Activities. — Only one normally active individual has been under observation. 

 This was swimming rapidly in anticlockwise spirals of a radius not exceeding 

 several lengths of the body, without rotation except for an occasional somer- 

 sault. During this period, and subsequently when the circus motions slowed 

 down, the prod was incessantly repeating its rhythmical contractions with brief 

 intermissions. 



After about thirty minutes under the cover glass the contractions slackened 

 in vigor and slowed down from the earlier rate of 80 per minute, became less 

 regular, and of smaller amplitude, and finally ceased. Shortly after this the 

 contracted prod was detached at its base l)y local cytolysis and speedily disin- 

 tegrated, with only a few circular and longitudinal fibers remaining intact for 

 a brief time. 



The behavior of this strange organ was observed for about two hours before 

 it was cast off and underwent immediate cytolysis. When first observed the 

 animal was very active, swinuning about in anticlockwise spirals. When the 

 spiral circling ceased temporarily the tentacle still kept up a continuous, 

 rhythmical, alternating retraction and protraction without cessation or modifi- 

 cation, except as interfered with by the substrate or other o})stacles, or by the 

 locomotor activities of the animal. When first timed, at a stage of somewhat 

 slackened activity, these recurrent thrusts of the prod were carried on at the 

 rate of one every 0.75 second. The regularity of the action was remarkable 

 and the continuity of it equally impressive and no less exasperating when one 

 was attempting to get a sketch, to say nothing of a camera outline, of this 

 extraordinary animal. 



The action was continued whether in contact with the sul)strate or not. In 

 case the extending tentacle met the resistance of another body this was vigor- 

 ously thrust awa}' if it was a small one. If, on tlie other hand, it was larger, as 

 in the case of the carapace of a copepod, the liody of the Erj/fhropsis was itself 

 pushed away at once by the vigorous thrust of the prod. The terminal stylet 

 exhibits considerable rigidity under such impacts. The result when the prod 

 met the substrate was e(|ually eifectivc. When lying ()l)Ii(iU('l>- mi its side the 

 tip of the prod was in contact with the glass and this contact was sufficient 



