CELL SIZE AND METABOLIC ACTIVITY IX AMPHIBIA. 365 



It is found that these divisions vary in width from 5.8 per cent, 

 below the mean to 5.6 per cent, above it. With such wide varia- 

 tions between the different divisions of the micrometer, the 

 question naturally arises as to whether the entire micrometer 

 may not be inaccurate. As a third check on the method the 

 dimensions of corpuscles as measured by means of the scale 

 were compared with the dimensions of the same corpu>cle- 

 m asured by means of the filar micrometer. It was found that 

 the scale is less accurate for individual corpuscles, because it i> 

 impo>sible to measure with it to an accuracy of less than (mi- 

 micron, but the average of a series of measurement- \>\ the \\\ 

 iin-thnd- ^ave closely parallel results. 



2. In the- Amphibia the size of individual red blood cell- in 



ilu -a me animal varies so widely that averages only partly repie- 



i the peculiarities of the different species. In many cases 



( H\KI iu. Variation in red blood cell size for Amphiuma (-..In! li.ic-i and 

 A'.niu ciitt-^iitinti il>mk.-n line). Abscissa, dimensions in micra; ordinal*.-, per- 

 o-m.iL;i- \ ti't.il i "i pii-i.li-- measured. Two curves are given for -a> li -|i<-cies, 

 one representing tlu- l<>nn diameters of corpuscles, and the oth.-r th<- -li-.rt diann -t< -r-. 



the range of \ariat i<>n in size is just as char.icteri-tic as the 

 average size. For this reason Table IV. has been prepared to 

 show the range of size variation in each species. In main < . 



