Il8 J. PAUL VISSCHER. 



rial. There are at least several hundred of these structures, all of 

 which are arranged in a band extending from the mouth to the tip 

 of the proboscis, approximately in the mid-line of its oral surface. 



There has been much discussion concerning the nuclear condition 

 of this organism, but recent investigators appear to be agreed that 

 Dileptus possesses a distributed nucleus. An account of this con- 

 dition will be omitted here, as it is planned to present a discussion 

 of the nuclear phenomena during the life history of this organism 

 in a separate paper. 



Dileptus is never at rest. It is always swimming, as a rule quite 

 slowly unless disturbed. In cultures it is observed to spend most 

 of its time swimming slowly just above the debris at the bottom 

 of the dishes. Apparently a like condition obtains in nature, for 

 if Dileptus is found in a pool, samples taken from near the bottom 

 contain many more specimens than those taken at higher levels. 

 It is observed to progress with its posterior end close to or in 

 contact with the bottom, while its anterior end is always at a 

 noticeable elevation. It proceeds with its proboscis ahead, con- 

 tinually waving it now this way, now that, as if in search of food. 

 It also rotates slowly on its longitudinal axis. This rotation, in 

 connection with the searching movements of the proboscis, enables 

 it to explore a very large area. 



In January, 1919, a few specimens of Dileptus gigas appeared 

 in an old " paramecium-culture " in which active fermentation had 

 long since ceased. It can not live long in any culture in which 

 active fermentation is taking place, nor can it thrive in cultures 

 rich in organic food supply. Consequently, very dilute infusions 

 were made, and these were usually inoculated with Euglena gracilis 

 before introducing Dileptus. In this manner the original culture 

 was kept for more than fifteen months. 



In nature I have found them in the large pond on the Home- 

 wood Campus of the Johns Hopkins University, Baltimore, and 

 also in the " school-house " pond near the Biological Laboratory at 

 Cold Spring Harbor, L. I. They were found also in the Cedar 

 Swamp pond at Woods Hole and in the outlet channel of Creve 

 Coeur Lake near St. Louis, Mo. In all these ponds at the time 

 Dileptus was found there was but little organic decay taking place 

 and the water was " relatively pure." 



