Donaldson, Nervous System of the\Frog. 331 



X. Growth. 



At the present time observations on the weight of frogs at 

 different known ages, are still wanting. 



It seems probable that enlargement occurs in the frog during 

 the late spring and early summer, and by analogy, we should ex- 

 pect the increase in length to occur before the most active in- 

 crease in weight. These statements, however, await demon- 

 stration. 



From the examination of Chart i, it is at once evident that 

 the weight of the central nervous system increases so long as 

 the weight of the entire body increases. The form of the 

 curve also shows that after the frog has attained a body-weight 

 of about 75 grams the increase in the weight of the central 

 nervous system becomes slow. 



Although we have no data as to the time relations of these 

 growth changes, something can be inferred from the foregoing 

 records as to the axes along which the enlargement takes place. 



To illustrate this, there is given below in Table 8, the 

 weight in milligrams of an average millimeter of both brain and 

 spinal cord. Also in another column the square root of the 

 number representing this weight. 



The cases chosen are the same as those in Table i. 



TABLE 8. 



Weight in Square root Weight in Sq. root of 



Body mgms. of of preceding mgms. of i mm. preceding 



weight 1 mm. of brain number of spinal cord number 



For the purpose of comparison such as is made in Table 8, 

 we assume the mass of the brain and spinal cord to be moulded 

 in the form of a prism with a square base, the long axis of 

 which geometric figure is assumed to be equal to that of the 

 part observed. In such a figure, each millimeter taken on the 

 long axis will have the same weight. 



In Table 8, the weight of one millimeter of brain or spinal 



