1917] Kofoid-Sivezy : On the Orientation of Erythrapsis 91 



ventral surface drawn as though on the dorsal side with resulting reversal of 

 symmetry as determined by the relative sizes of posterior horns. 



Fig. 3. Cochlodinium pulchellum Ijehour, aHer 'Lehour (1917). X 964. Note 

 that the direction of the spirally twisted girdle is from the left side of the 

 body across to the right, that is, the girdle forms a descending right spiral. The 

 sulcus is only partially and incorrectly drawn. 



Fig. 4. Cochlodinium pulchellum Lebour, correctly drawn from life. Original. 



For example, Daday (1888) described and figured Ceratium gravidum 

 with a girdle having the opposite course. This, however, is due merely 

 to an inadvertent oversight in observation and drawing. The ventral 

 area of Ceratium is usually deeply impressed into the ventral face. 

 Viewed dorsally its outline becomes distinct as one focuses down to 

 secure an optical section of the midbody. If the outline of the body 

 is then drawn from the dorsal side and the ventral plate also drawn, 

 the symmetry of the organism is reversed and the girdle appears to 

 pass from its proximal end distally on the ventral face to the right of 

 the body over dorsally to the left, thus forming a right spiral instead 

 of a left one. 



Another example of reversal of symmetry by drawing the lower 

 surface of the body as though it were the upper is found in Miss 

 Lebour 's figure (1917) of Cochlodinium, pulchellum in which the direc- 

 tion of the girdle is reversed although in the description of the species 

 no notice is taken of this profound structural modification. It appears 

 to be only an inadvertent lapse in drawing. We have found that this 

 species has the normal structure at La Jolla and offer for comparison 

 a figure with the customary presentation of the upper surface (fig. 4) 

 in which there is in consequence no reversal of symmetry. 



During the examination of many thousands of dinoflagellates we 

 have found not a single instance critically determined of such reversed 

 symmetry in nature, although one easily falls into the trap of making 

 such reversed drawings and failing to note the fact at the time. No 

 such reversals should be accepted as valid unless critically verified 

 on the living specimen showing the flagellum in action, and even then 

 one should be on the lookout, in Gymnodinioidae, for transverse flag- 

 ella thrown out of place into the anterior extension of the sulcus. It 

 is, of course, possible that such reversals of symmetry might occur in 

 nature, but evidence of their occurrence is lacking. 



The so-called dextral and sinistral forms, described by Mangin 

 (1911) do not involve the reversal in direction of the transverse flag- 

 ellum and girdle above noted, but only the change from a descending to 



