Donaldson, American and European Frogs. 



135 



R. pipiens has still the heaviest cord, but R. temporaria, with 

 the hghtest entire central nervous system, has a spinal cord nearly 

 as heavy as that of R. pipiens, while the cord in Rana esculenta is 

 distinctly lighter than in the other two species, having on the aver- 

 age 94 per cent of the weight of the cord in R. pipiens. 



TABLE II. 

 Weight of the brain and spinal cord in grams. Averages from groups of three. 



To show the relative weight of the brain as compared with that 

 of the cord in these three species, we may use the ratio obtained 

 by dividing the brain weight by the cord weight. These ratios 

 are given in the following table : 



TABLE 12. 

 Ratios of the weight of the brain to the weight of the spinal cord. Averages 



from groups of three. 



Body Weight. Ratio. 



R. pipiens 14.9 2.33 



23.2 2.22 



30.8 2.32 



43.2 2.28 



R. esculenta , 15.9 2.29 



22.0 2.22 



35.0 2.09 



40.2 2.05 



R. temporaria ir.n 2.IC 



23.1 1.86 

 28.0 1.87 



31.3 1.87 



