GONADS AS CONTROLLERS OF CHARACTERISTICS 141 



Litter 6 AIBI 

 I. Spayed female with testis graft. 

 II. Spayed female with testis graft. 



III. Normal female (control) 



IV. Castrated male with ovary graft. 

 V. Castrated male with ovary graft. 



VI. Spayed female with testis graft. 

 VII. Normal male (control) 

 VIII. Castrated male with ovary graft. 

 IX. Normal female (control). 



BODY WEIGHT AND BODY LENGTH 



It is unfortunate that the distinguishing somatic characters 

 of the male and the female rat are not more sharpl}^ marked 

 than they are. However, the studies of Stotsenburg ('09, '12, 

 '13), King, and others^ show that within certain limits the growth 

 curves (body weight) and the body lengths normally afford 

 criteria for a distinction between the two sexes. Steinach hsa 

 placed considerable emphasis upon these weight and body-length 

 relations of his feminized males and masculinized females as 

 being indicative of maleness and femaleness. It is the opinion 

 of the writer, however, that such slight differences in weight 

 are but poor criteria of maleness or femaleness under abnormal 

 conditions. It is true that the normal curve of growth for male 

 rats is considerably above that for females, but it is decidedly 

 unreliable to choose two or three rats at random and classify 

 them sexually on the sole basis of weight; there is too much 

 tendency for variation even among rats of the same litter for 

 it to be reliable. Also a slight pathological difference may pro- 

 duce a relatively great change in weight even though the rat is 

 in apparently good health. Too many operated animals are 

 required to make the factor a convincing one. But of more 

 importance than this, perhaps, is the fact made known by Stot- 

 senburg that early castration of male rats does not influence the 

 subsequent growth curve, while early spaying of female rats re- 

 sulted in an increased growth curve over that of the normal female 



* Complete references of work done on rats have been compiled by Donald- 

 son in a book 'The Rat' (Memoirs of The Wistar Institute of Anat. and Biol., no. 

 6, 1915). 



