Henky H. Donaldson 



11 



drops rather rapidly, about 5 per cent., to the end of June. In July and August it 

 remains, with slight fluctuations, comparatively, constant, and at the beginning of 

 September falls off from 2 per cent, to 4 per cent, as the frogs enter upon hibernation. 

 These observations of course apply strictly only to frogs subjected to the climatic con- 

 ditions found in Chicago and the neighborhood within a radius of one hundred miles. 



In the preceding Table III we have indicated the tabular number of the frog, the 

 weight of whose nervous system has been corrected, the date at which the initial 

 observation was made, and the amount of the correction. The correction is entered 

 in this table as a percentage of the observed weight, the -|- sign indicating that the 

 amount was added and the sign — that it was subtracted. 



In Table IV the observed weight of the nervous system which is there given for 

 these cases is the corrected weight, and the fact that it is a corrected weight is indi- 

 cated by the small letter (c) which follows the entry. 



The other records in Table IV are from frogs killed in July and August, and are 

 therefore classed as midsummer frogs. It will be recalled that in the case of Rana 

 virescens the formula for calculating the weight of the central nervous system is the 

 same as that for the bullfrog, except that the constant, C, is 28 instead of 30. The 

 formula reads, therefore: 



C.N.S. = (Log T^ X f/L) 28. 



It is with this formula that the calculations appearing in Table IV have been made. 

 The construction of Table IV is similar to that of Table I. 



On applying to the records in Table IV the same tests as were used in the case 

 of the bullfrog. Table I, we obtain results which are in some respects more satisfac- 

 tory. It will be seen that the average weight of the central nervous system as calcu- 

 lated is exactly equal to the average weight observed. Further, if we divide the 

 twenty-eight records into three groups of nine, nine, and ten, respectively, indicating 

 the groups as A, B, and C, then the percentage differences for each group are seen to 

 be also small — Table V. 



TABLE V 



To show the average percentage differences in the values of the observed and calculated weights of the 

 central nervous system in three groups, formed from Table IV. 



This shows a maximum deviation for Group B of 2 per cent., but it seems probable 

 that a series of records based on averages would coincide more closely than this. On 



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