GROWTH AFFECTED BY FEEDING DUCTLESS GLANDS 335 



19. Epididymi (tables 7 and 9) 



a. Controls. Few data are available for comparison. Jackson 

 ('13) states that after the age of puberty the epididymis weighs 

 about one-third as much as the testis, and in extreme cases 

 one-half. In my series (tables 7 and 9) the eipdidymi average 

 about one-fourth as heavy as the testes in the younger (0.28 

 per cent of net body weight), and about one-third as heavy in 

 the older group (0.34 per cent of net body weight). Some of 

 the variability in the weight of the epididymis is due to the 

 difficulty in removing the fat associated with it. 



h. Thyroid groups. The epididymi in the thyroid group, 

 like, the testes, appear slightly larger than in the control rats 

 (tables 7 and 9). It is doubtful whether they are stimulated 

 in growth by the thyroid treatment, however. 



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

 as was true in regard to the testis, the variations in comparison 

 with the controls are probably not significant. 



20. Pineal body {tables 6 to 9) 



a. Controls. No attempt has hitherto been made to deter- 

 mine the normal weight of this small organ in a large series of 

 albino rats. Eiedl ('13) gives the weight as 0.0020 g., which is 

 considerably higher than the average weights in my series 

 (0.0011 g. in the females and 0.0013-0.0014 g. in the males, 

 tables 6 and 7). The weight values obtained vary greatly on 

 account of the extremely small size of the gland. Relatively 

 (tables 8 and 9) there seems to be no significant difference 

 according to sex or age, although the percentage weight ap- 

 pears to be somewhat less in the animals of greater body 

 weight, and this to some extent is due to age. Recently, from 

 data secured through the kindness of Dr. Donaldson and Dr. 

 Hatai, I note that the values obtained for the pineal body in 

 rats at the Wistar Institute agree fairly closely with mine. 



b. Thyroid groups. The pineal body in the thryoid-fed rats 

 (tables 8 and 9) averages in relative weight somewhat heavier 

 in the various groups than in the corresponding controls. The 



