444 JoiiriKi! of Ci>i)i[^aralii'c Ncuroloi^y and PsycJioIogy. 



as I hav^e observed, is always ove)' to tlie left, when the anterior 

 end is directed away from the observ'^er. That is, the upper 

 surface is continually passing to the observer's left (the lower 

 surface of course to his right).' Before using the stereoscopic 

 binocular I supposed that the revolution was sometimes over 

 to the right, sometimes over to the left (Jennings, 1899, p. 

 316). But observation of thousands of cases since this instru- 

 ment was used has never shown a single exception to the revo- 

 lution over to the left. I have repeatedl}' known observers 

 working with the usual monocular microscope to assert that 

 part of the Paramecia in a gi\'en culture were revolving over to 

 the right, but on examination with the stereoscopic binocular 

 they invariably became convinced that there was no exception 

 to the revolution oxer to the left. The appearances shown by the 

 monocular microscope are very deceptix'e in such phenomena, 

 and 1 do not believe that observations with it even by practiced 

 observers are reliable on this particular point. 



The revolution is still over to the left when the animals are 

 swimming backward. This is contrar)' to the statement made 

 in the second of my "Studies" (Jennings, 1899, p. 316), when 

 I was working with the monocular microscope. But the binoc- 

 ular leaves no doubt upon this point. When the forward move- 

 ment is reversed, the direction of rotation is not reversed. 



The oral groove of Paramecium always passes, if the oral 

 side is down and the anterior end away from the observer, from 

 the right behind to the left in front (as represented in Butschli, 

 1889, PI. 63, F'ig. 1 a). Many observers have reported Para- 

 mecia in which the direction of the groove is "rexersed," running 

 from the middle obli(]uel\- to the right instead of to the left. 



' 'I'heif is 110 {general a^reeincnl as to iht- designation of thi- diicclion of a 

 spiral. The above inetliod seems most convenient for free swimming organisms, 

 since it gives tlie results of immediate observation, and other methods of desig- 

 nation usually have to be translated, for practical purposes, into this one. If we 

 used the method of designation projjosed by N.EGELl (i860), the spiral of Para- 

 mecium rises from south to west. If we designate the direction of rotation by 

 the method used in spiral cleavage, imagining a small observer situated in the 

 long axis of Paramecium witii head toward the anterior end (KoFoui, 1804, ]i. 

 180), then we must sav thai the rotation is to the right. 



