336 E. R. HOSKINS 



difference is not constant in every litter so that, although it is 

 possible that the thyroid medication increases the weight of 

 this organ, the data are insufficient for a final conclusion. 



c. Thymus, hypophysis, and pineal groups. On comparing 

 the relative weights of the pineal body in these groups, the re- 

 sults in the case of the thymus-fed and hypophysis-fed are very 

 inconstant. In the pineal-fed, as in the thjrroid-fed rats, the 

 pineal body appears usually increased in relative weight. The 

 difference in weight is not constant in every litter, and hence is 

 of doubtful significance, in all of these three groups. 



21. Hypophysis {tables 7 to 10) 



a. Controls. In absolute weight the hypophysis in both male 

 and female rats in my series agree fairly well with Donaldson's 

 tables for rats of corresponding body length or body weight (tables 

 4 and 5). There is a sexual difference in the weight of this or- 

 gan, as discovered by Hatai ('13). As seen in tables 8 and 9, 

 the average percentage of the net body weight for the hypophysis 

 is about 0.0066 per cent in the females and 0.0039 per cent in 

 the males (not much change according to age or body weight). 

 Thus the hypophysis, like the suprarenal body, is in the adult 

 rats relatively much larger in the female. 



6. Thyroid groups. . On comparing the thyroid-fed animals 

 with the controls (tables 8 to 10), there appears a very slight 

 decrease in relative weight of the hypophysis in the female groups. 

 In both male groups there is a decided increase in the weight 

 of the hj^ophysis. With Donaldson's method of comparison 

 the decrease in absolute weight in the older and younger female 

 groups is 11.5 and 8.8 per cent respectively, and the increase 

 in the corresponding males is 21.3 and 18.0 per cent (table 10). 

 These results may be interpreted as indicating a sexual differ- 

 ence in the effect of thyi'oid feeding upon the hypophysis, the 

 effect being most marked in the males. The thyi'oid-feeding 

 therefore tends to reduce the normal difference between the 

 sexes in the weight of the hypophysis. 



