The Life-History of Hypotrichous Infusoria. 589 



gives the greatest variation which could possibly occur, and by 

 averaging the maximum and minimum points of each day for ten- 

 day periods the result is quite satisfactory for comparative work. 



For the purpose of following as closely as possible the changes 

 in cell structure during the life of the cultures, permanent prepa- 

 rations of individuals from different lines were made from time 

 to time. Here again I employed with little change the method 

 used by Calkins, which is briefly as follows : The specimen to be 

 preserved is isolated by means of a fine-pointed pipet on a clean 

 depression slide (which is kept just for this purpose) with as little 

 of the culture-medium as possible. To this is added three or four 

 drops of bichlorid of mercury in saturated solution with 5 per 

 cent of glacial acetic acid. After about five minutes the specimen 

 is transferred to another slide and a few drops of 75 per cent 

 alcohol is added. A slide is now smeared with a trace of egg- 

 albumin and the specimen is taken from the 75 per cent alcohol 

 and gently spurted onto the albumin. After a short time, w^hen 

 the alcohol has coagulated the albumin, the slide with the speci- 

 men adhering to it is transferred to a jar of 75 per cent alcohol and 

 is thereafter treated by the ordinary slide method. 



For staining, Ranvier's picrocarmin was used, although 

 Delafield's hematoxylin gives quite satisfactory preparations. 

 Clearing was done with xylol, and damar was used in mount- 



For convenience in description the main cultures are designated 

 by letters, and the individual lines (four in number) which make 

 up each of these cultures are designated by figures. Thus, the 

 two cultures of Oxytricha fallax are designated respectively A 

 and B, and the lines under them as A-i, A-2, A-3, A-4, and 

 B-i, B-2, B-3, B-4, In each case the culture was started by 

 isolating one wild individual and when this had divided twice, 

 giving four individuals, these were isolated to start the four lines. 

 These four lines thereafter were kept distinct except in cases 

 where one died out through accident or through the isolation of a 

 weak individual, in which case its place was supplied by a speci- 

 men from one of the three closely related lines. Of course, the 

 more lines of a culture that are carried on, the closer their average 

 rate of division will approach the true one for the culture. I have 

 found that four lines is all that can be reasonably carried without 

 undue labor and the average here is probably near enough to give 



