378 Dr. R. Pearl. A Biomedical [Nov. 15, 



measured from material in the Zoological Laboratory of the University of 

 Michigan, collected by Professor D. C. Worcester. They all came from a 

 single culture set with decaying plant material and pond water. Series AA 

 includes 200 pairs of conjugants, Series F E 70 pairs, and Series F L 77 pairs. 



Series. 



Dates of measurement. 



A 

 C 



D* 

 E 



August 15, P.M. — August 18, noon, inclusive 

 „ 24, A.M.— „ 26, p.m., „ 



„ 30 



September 6 



Number 

 of conjugants 

 measured. 



Number of 

 non-conjugants 

 measured. 



105 pairs 

 101 „ 

 16 „ 



210 

 202 

 32 

 132 



For further details regarding the measurements, culture histories, etc., the 

 complete paper must be consulted. 



2. An examination of the variation constants shows that Paramecium is 

 relatively slightly more variable in breadth than in length of body, though 

 the difference is not large. For the variation in length the coefficients of 

 variability for different series (including several other long series besides 

 those collected in this work) are found to cluster well together about a value 

 of 8 to 9 per cent. This is a much lower value than has been found by 

 other workersf for variation in similar size characters in organisms with firm 

 exoskeletons. In the characters studied Paramecium follows the same 

 general laws which have been shown to hold for continuous variation in 

 higher forms. 



3. It was found that conjugants are markedly differentiated from non- 

 conjugants living in the same culture in both type and variabilitj'. This 

 differentiation includes all the characters studied. An idea of its extent 

 and direction may be gained by an examination of the following table. 

 In it are given {a) the absolute differences between conjugants and non- 

 conjugants in respect to the character and constant designated; (b) the 

 probable errors of these absolute differences ; (c) the relative differences 

 defined as the percentage which the absolute difference is of the non- 

 conjugant constant in each case. The absolute differences are taken as 

 positive when the non-conjugant constant is greater. Only two series 

 (A and C) are taken here as illustrations. In the complete paper similar 

 data for other series are given in detail. 



* Series D and B (vide infra) include only a few individuals, because at the time they 

 were collected no more conjugants were to be found in the cultures from which they 

 came. 



t For detailed references, see complete paper. 



