GROWTH OF AMPHIBIA AFTER THYROIDECTOMY 23 



lobes and minor subdivisions. The organ varies in size con- 

 siderably. Before the time of metamorphosis it is clearly smaller 

 in the thyroidless than in control larvae of the same size but 

 older. The average difference is slightly less than that indicated 

 by figures 32 and 33. This difference in size possibly indicates 

 that in the thyroidless larvae the metabolism is less rapid than 

 that of the controls, since the size of the liver is ordinarily pro- 

 portional to the rate of metabolism (Hoskins, '16). The thy- 

 roidless larvae grew more rapidly than the controls, however, and 

 one would expect them to have large livers. 



During metamorphosis the liver and gall bladder decrease in 

 size as much as or more than the whole body (fig. 34), as is to 

 be expected since the young frog has a lesser total metabolism 

 than the larger tadpole from which it is transformed. Changes 

 in form of the liver also occur during metamorphosis (fig. 34). 

 The groove formed by the coil of the intestine that was embedded 

 in it disappears and the entire organ becomes more compact. 

 The three lobes become very distinct. The liver grows to a 

 considerable size in the larger thyroidless larvae (fig. 35) both 

 actually and relatively, and there is a very definite approach 

 on the part of this organ to the shape of the frog's liver (fig. 34) . 

 The three lobes becoftie well marked, but one is still grooved by 

 the coil of the intestine already referred to. After the thyroid- 

 less larva has ceased active growth, the liver tends to become 

 smaller so that in the second year of its life the thyroidless larva 

 has, in general, a relatively smaller liver than thyroidless larvae 

 of the first season of the same size of body. This decrease in 

 the size of the liver that occurs in the older specimens is probably 

 accounted for by a decreased metabolism. 



Hypophysis. The hypophysis of the frog is composed of a 

 glandular portion developed from the ectoderm and a non- 

 glandular part, the infundibulum formed by the brain. The 

 former portion becomes subdivided into three secondary lobes 

 corresponding in position with those of fishes. We shall refer 

 to these secondary lobes by the terms generally used for hypoph- 

 ysis of fishes, namely, anterior, superior, and inferior lobes. 

 Of these three lobes, the inferior is the largest, shows the earliest 



