DoNALDsoN-ScHOEMAKER, Ncfvous System of Fvogs. 115 



The foregoing table is constructed from data extracted 

 from Table VII. The body-weight as given in this and the 

 other special tables will always serve for the identification of a 

 record. The numbers representing the weight values of the 

 brain and spinal cord correspond to those found in Bull-frogs 

 of the same weights. They show that the proportional weights 

 of both the brain and spinal cord suffer a steady diminution ; 

 the value for the brain falling the more rapidly. When the 

 sexes are contrasted in virescens, the slightly heavier central 

 nervous system in the female increases the percentages by a 

 corresponding amount, but the difference does not need to be 

 discussed in detail. 



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

 Spinal Cord. 



The fact that the proportional weight of the brain under- 

 goes the more rapid decrease, brings with it the result that the 

 ratio of the weight of the brain to that of the spinal cord di- 

 minishes as the weight of the frog increases. 



Using the same cases employed in Table V, we have the 



following : 



TABLE VI. 



Body weight Ratio of the weight of the brain 



in grnis. to that of the spinal cord. 



3-34 2.53 



38.16 2.12 



76_54 1^93 



This series of ratios corresponds with what has been 

 found for the Bull-frog, though for frogs of the same weight 

 the corresponding ratios are always lower in R. virescens. 



In the Bull-frog we have seen that a diminution in this 

 ratio goes along with the maturing of the central nervous sys- 

 tem, and we may therefore interpret the smaller numbers found 

 in virescens as meaning that in our largest frog (of ^6 grms.), 

 the brain has already attained the same weight relation to the 

 cord as is found in the largest of the Bull-frogs, which may 

 have a body-weight of more than 400 grms. 



