GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 317 



slight relative decrease in weight in the thyroid males of higher 

 dosage, but not in the females. 



c. Thymus, hypophysis and pineal groups. In all these groups, 

 the weight of the eviscerated body is very close to that of the 

 controls (muscle-fed). The variations are slight and probably 

 insignificant. 



4. Integument (tables 6 to 9) 



a. Controls. The average relative (percentage) weight of 

 the integiunent is relatively fairly close in the various groups of 

 both sexes. In general, the percentages range between 21 and 

 24 per cent of the net body weight, the value for the male rats 

 being slightly greater than for the females, due possibly to the 

 presence of a greater amount of fat in the latter. This is some- 

 what higher than that observed by Jackson and Lowrey ('12), 

 by more than 4 per cent of the entire net body weight, and is 

 2 per cent of the entire body weight higher than that observed 

 by Jackson ('15). These differences are probably due largely 

 to the varying amount of fat (or muscle) present in the 

 integument. 



h. Thyroid group. In the thyroid rats of each sex the integu- 

 ment appears usually very slightly lighter in weight than in the 

 controls, owing probably to loss of fat. Jackson ('15) has shown 

 that during inanition the skin loses greatly in weight (probably 

 due chiefly to loss of fat) but that the relative (percentage) 

 weight remains unchanged in adults. 



c. Thymus, hypophysis and pineal groups. In these groups, 

 the differences in weight of the integument, as compared within 

 each group and with the controls (muscle-fed), are well within 

 the limits of normal variation. 



5. Cartilaginous skeleton (tables 6 to 9) 



a. Controls. The relative weight of the 'wet' cartilaginous 

 skeleton averages about 7.6 per cent of the body weight in the 

 older females, and about 6.6 per cent in the older males. The 

 skeleton in the younger females averages about 6.8 per cent of 



