EXTIRPATION OF ANTERIOR LOBE OF HYPOPHYSIS. 1 29 



It is clearly evident from the above figures that tadpoles de- 

 prived of the hypophysis produce far less colloid substance in 

 their thyroid glands than do the normal controls. This is a 

 markedly constant point of difference. This would seem to be 

 an index of its secretory activity in the two cases; although the 

 recent work of Bensley would cast doubt upon the value of the 

 colloid accumulation as an index of the secretory activity of the 

 thyroid. 



In the 16.5 mm. and 21.5 mm. stages, the thyroid is actually 

 larger in the operated individuals than in the corresponding 

 controls while in the 24 mm. stage the thickness dorso-ventral 

 dimension is on the contrary almost twice as great in the control 

 as in the operated specimen. The material is too scanty to 

 enable one to draw positive conclusions upon this score from my 

 work alone. It may be well to point out however that Adler, 

 Smith and myself are in agreement regarding the effect of the 

 removal of the hypophysis upon the development of the thyroid 

 gland and regarding the relatively small amount of colloid pro- 

 duced in them. 



I should hesitate to attribute the failure of the limbs to develop 

 in operated tadpoles to the lessened activity of the thyroid 

 resulting from the absence of the hypophysis. This question 

 must be tested by more crucial experiments than any as yet 

 applied. 



In general the thymus gland is larger in the operated tadpoles 

 than in the controls. The differences are not constant nor are 

 they striking in the face of the general variability of this organ. 

 It only seems safe to state that the thymus is not adversely af- 

 fected in size or structure by the removal of the hypophysis. 



The gonads show a large amount of variation in size and form. 

 The absence of the hypophysis does not produce any apparent 

 modification in them in the stages studied. The germ cells, sex 

 cords and the various structures of the gonads appear to be quite 

 unmodified by the operation. The operated tadpoles of 21.5 

 mm. and of 24 mm. stages after sexual differentiation are both 

 males. It is thus impossible to tell whether there is any difference 

 in the effects upon the two sexes. This point of the effect upon 

 the gonads must be carried out in future experiments reaching 

 to much later stages and involving far larger numbers of tadpoles, 



