377 



A Biomedical Study of Conjugation in Paramecium. 

 By Raymond Pearl, PhJ). 



(Communicated by Professor Karl Pearson, F.R.S. Received November 15, — 



Read December 7, 1905.) 



(Abstract.) 



1. A study of variation and correlation in conjugating and non-conjugating 

 specimens of the common ciliate infusorian, Paramceeium cmidaium, was 

 undertaken for the purpose of obtaining answers to the following questions : — 



a. Is the portion of the Paramecium population which is in a state of 

 conjugation at a given time differentiated in respect of type or variability 

 or both from the non-conjugating portion of the population living in the same 

 culture at the same time ? 



b. Is there any tendency for like to pair with like (" homogamy ") in the 

 conjugation of Paramecium, and if so, how strong is this tendency ? 



The material on which this paper is based is comprised in eight series, 

 taken from three different cultures at different times, and includes altogether 

 the measurements of 1894 individual Paramteeia. The characters studied 

 were length and greatest breadth of the body, length-breadth index, and 

 the difference in length between the two individuals of a pair of conjugants. 

 In the measuring conjugant pairs were taken quite at random, and then in 

 each case the two undistorted non-conjugant individuals which were lying 

 nearest in the field of view of the microscope to the conjugant pair were 

 measured. This procedure was followed to avoid any sub-conscious bias in 

 choosing non-conjugants. 



The cultural history of the different series may be summarised as 

 follows : — 



Series A, G, D, and E. — These series all came from a single culture in the 

 Zoologisches Institut, at Leipzig. This culture was set with dry hay and 

 pond water, July 25, 1905. The dates of collection and measurement and 

 number of individuals in each series are given in the table on p. 378. 



Series B. — This series came from another culture at Leipzig set in the same 

 manner as the one just mentioned. Conjugants were found on August 22, 

 but in very small numbers. On the next day only two pairs of conjugants 

 were found, and after that none at all. So that, all told, Series B included 

 only 12 pairs of conjugants and 24 non-conjugants. 



Series AA, F E , and F L . — These series included only conjugants. They were 



