$i6 Journal of Comparative Neurology. 



central system according to sex has been observed, but it would 

 require a large number of observations on frogs of the same 

 body-weight to properly demonstrate any difference of this sort. 

 The records therefore have not been separated according to sex. 

 Table i also shows that the proportional weight of the 

 brain decreases more rapidly than that of the spinal cord. This 

 is again shown, in a slightly different way, in Table 2, in which 

 the smallest and largest frogs of the series are compared di- 

 rectly. 



TABLE 2. 



Body weight Weight of Brain Weight of Spinal 



in grams. in grams. Cord in grams. 



1.32 .025 .009 



313.50 .215 .106 



On comparing the brain weights in Table 2, there is found 

 (by dividing the larger by the smaller) an increase of over eight 

 fold, whereas the spinal cord has increased nearly twelve fold, 

 thus confirming the statement concerning the more rapid en- 

 largement of the cord. 



The foregoing figures are based on single observations and 

 hence are liable to vary as the individual observations vary, but 

 the individual variability is so small that this general relation is 

 affected by it to only a trifling extent. 



From the difference in the rate of enlargement, it follows 

 that the ratio of the weight of the Brain to that of the Spinal 

 Cord normally decreases as we pass from small, to large frogs. 



Using the same observations as were employed in Table i, 

 and recording only the number of times that the brain exceeds 

 the spinal cord in weight, we obtain the following : 



TABLE 3. 



This change in the relative weight of the brain has been 

 found in all vertebrates in which the relation has been studied. 



