PHYSIOLOGICAL PROPERTIES OF THE GONADS. 309 



animals is surprising from the lack of more appreciable differences. 

 In fact, the most clearly disproportionate length occurred in the 

 spayed females. The bones of this group seem to reflect a specific 

 effect of the absence of the ovarian secretion. The literature leads 

 one to believe that differences between normal male and castrated 

 male bone lengths is pronounced and easily detected. But the 

 difference in lengths among the different groups of this experiment 

 was so slight that careful computation was necessary to reveal it ; 

 the difference was so small that it appears almost insignificant. 



Striking as may be the influence of the internal secretions of 

 the sex glands on some characters in certain animal forms, it 

 appears difficult and often impossible to discover characters in 

 ordinary laboratory animals that are of sufficient difference and 

 constancy in the two sexes to be capable of analysis by experi- 

 mental procedure. And many of the characters cited in the litera- 

 ture supposedly offering a demonstration of the power of sexual 

 secretions to effect modifications in the opposite sex fall to the 

 ground if subjected to critical analysis. In the writer's opinion 

 the character of weight reactions in guinea pigs belong to this 

 group. 



XI. SUMMARY AND CONCLUSIONS. 



On the basis of observations on the guinea pig, herein reported, 

 the following conclusions are drawn : 



1. The curve of growth for normal male guinea pigs is consist- 

 ently above that for normal females up to the end of the first year, 

 when the two curves practically coincide. 



2. Gonadectomy is followed by a decrease in the growth curves 

 for both sexes; however, by the 3OOth day spayed females have 

 reached the weight of normal females, and at the end of one year 

 are i per cent, heavier than the normals. 



3. The relative weight of a guinea pig is worthless as an indica- 

 tion of its sexual condition ; properly controlled groups of weights 

 may offer a debatable criterion of sex-gland effects, but random 

 comparisons indicate nothing. 



4. Total length of the animals correspond to total weights in 

 the order : normal males > normal females > spayed females ^ 

 castrated males. 



