Donaldson, Novoiis System of the Frog. 317 



For comparison we may take the observations on man and the 

 white rat. In man between birth and maturity, the spinal cord 

 increases about twice as fast as the brain. In the white rat 

 about three times as fast, while in the frog, as shown above, 

 the increase is only one and three tenths as fast. Thus it ap- 

 pears that in the frog the weight relations of the brain and spinal 

 cord undergo less change during later growth, than in either 

 the white rat or man. 

 II. Ratio of the Weight of the Brain to that of the Spinal Cord. 



In the Table 3, just given, this ratio shows a steady de- 

 crease, the individual observations being widely separated from 

 one another. If, however, consecutive observations are taken, 

 the variability in this ratio becomes evident. 



From the frog weighing 27.33 grms., to the one weighing 

 233.79 grrris., inclusive, there are in Table 7, twenty-one com- 

 plete records. These records, taken in the order of the body 

 weight, have been divided into three groups of seven each, and 

 the groups are here designated as A, B, and C. In Table 4, 

 are given the ratios for each case in each group and at the foot 

 of the column, the average for the entire seven cases forming 

 the group. 



TABLE 4. 

 Showing ratio of brain weight to the weight of the spinal cord. 

 Group A B C 



2.55 2.22 2.23 



2.46 2.46 1.96 



2.23 2.01 2.21 



2.32 2.41 2.02 



2.36 1.98 2.09 



2.35 2.07 2.21 



2.31 2.19 2.25 



Average 2.37 2.19 2.14 



Here again the average ratio is seen to decrease as the 

 frogs forming a given group increase in weight. To discuss, 

 however, the variations in the ratio occurring between consecu- 

 tive cases, it will be necessary first to state some of the condi- 

 tions influencing the weight of the central nervous system. 



