480 JENNINGS— HEREDITY IN PROTOZOA. [April 24, 



It is not necessary to emphasize the fact that since different 

 environmental conditions produce different dimensions, the coeffi- 

 cients of observed variation will be much increased by throwing 

 together specimens from dift'erent environments, or those taken at 

 different times from the same culture. Examples of this are seen 

 in rows 12, 15 and 20, Table XVIII. 



The question may be asked. How can we account for the large 

 coefficients of variation in given lots, taken all from the same envir- 

 onment (as in the various "rows" of Table XVIII.)? Surely, it 

 may be said, the age differences among the individuals are not suffi- 

 cient to account for coefficients of 12, 13, 20, etc., such as we actually 

 find. This is undoubtedly true, and it becomes still more striking 

 when we consider cases like Table XLI. (appendix), where the indi- 

 viduals are all of practically the same age, and all come at one time 

 from the same small watch-glass of hay infusion, yet we find the 

 coeffxients of variation to be respectively 6.389 and 14.615. The 

 considerable variation is to be understood only by realizing that even 

 a small mass of fluid constitutes a relatively large and varied envir- 

 onment for Paramecium. A watch-glass of hay infusion is a micro- 

 cosm to this animal. Bacteria gather on the surface, while they 

 may not be found on the bottom or through the middle. The bac- 

 terial zoogloea may become thicker at one edge than at the other, 

 owing to the accidents of the original distribution of the seed bacteria 

 or of the infusoria. Some of the Paramecia thus get more food 

 than the others, perhaps at a critical period of growth; they thus 

 get a start, which enables them perhaps to obtain more food than 

 the others, even under uniform conditions. Some of the individuals 

 get crowded away from the bacterial zoogloea, and remain against a 

 rough spot on the glass instead, where they get no food. In short, 

 even in a few drops of water the conditions are not uniform through- 

 out; some of the animals are well nourished, others poorly nour- 

 ished, and the results show in the variations of their measurements. 



The question whether some of the variations in such cases are 

 not congenital and hereditary will be taken up later; we shall find 

 little evidence that this is the case. 



It is clear that no particular coefficient of variation can be con- 

 sidered characteristic of a particular race, except as the conditions 



