178 Journal of Comparative Neurology. 



origin to it. Therefore what is shown in columns i and 3 is to 

 be expected, namely, that an increase in substantia grisea is 

 accompanied by a more rapid increase in substantia alba. Col- 

 umn 4, giving the ratios of the two substances, shows that for 

 the larger specimens the area of the substantia alba is approxi- 

 mately 5 times ?s great as that of the substantia grisea, while 

 for the smaller specimens it is 2 or less times as great. 



3. In the series of specimens the ratio of the area of the 

 section of the cell-body to the area of the substantia grisea 

 containing it decreases with considerable regularity from the 

 largest to the smallest specimen, but the decrease is not in pro- 

 portion to the variations in the areas of the sections of the cell- 

 bodies. 



These comparisons may be made in columns 7 and 5. Col- 

 umn 5 is derived from Table III and contains for each speci- 

 men the area of the section of the average large cell-body com- 

 puted from the mean diameters recorded there. Thus the areas 

 of the cell-bodies differ among themselves much as the diam- 

 eters from which they are derived. For a comparison of the 

 area of the section of the cell-body with that of the substantia 

 grisea, it was thought better to use only the area of that part 

 of the substantia grisea which contains the cell-bodies employed. 

 The amount of substantia grisea in the columnae posteriores 

 depends largely upon the amount of substantia gelatinosa pres- 

 ent. This latter varies greatly in relative amount in the differ- 

 ent individuals as w^ell as in different levels of the same individ- 

 ual and has necessarily nothing to do with either the size or the 

 number of the cell-bodies in the columnae anteriores. Then 

 to obtain what are considered the more expressive ratios, the 

 areas of the columnae posteriores were excluded. In column 



6 are recorded in each case the area of that part of the gray 

 figure ventral to a line drawn through the gray figure along the 

 dorsal border of the commissura grisea. The ratios in column 



7 are obtained by dividing in each case the area of this portion of 

 the substantia grisea by the area of the section of the average 

 large cell-body (column 5) and thus express the number of times 



