60 PIGMENTARY GROWTH AITTER ABLATION OF 



toad as in the albinous frog larvae. This is also true of their 

 response to a 'substitution' diet of anterior-lobe substance. 

 The growth rate of those toad albinos supplied with an hypo- 

 physial diet does not quite equal that of their normal brothers.'" 

 Neither has the administration of hypophysial extracts, residues, 

 and colloid given as clear results as in the frog tadpole (figs. 7, 

 8, 9). However, an unmistakable growth retardation is shown 

 by the albinous toad larvae supplied with the extracts arid 

 colloid, and the administration of the residues has caused a 

 distinct acceleration in growth rate as compared to their liver- 

 fed albinous mates. Table 4 gives the measurements upon which 

 the growth curves of the toad tadpole are based, and table 5, 

 the number of specimens used in the study. 



From a survey of these groups receiving the various hypo- 

 physial substances and liver it is evident that they are separable, 

 whether frog or toad larvae be used, into two distinct cate- 

 gories, both by the size attained and by the nature of their 

 growth curves. On the one hand is the group formed by those 

 larvae supplied with either the alcoholic or aqueous residues; 

 their growth curves are identical with that of the fresh anterior- 

 lobe-fed group; on the other hand is the group formed by the 

 larvae receiving Tethelin, aqueous extract and colloid; these 

 exhibit some variation in size, but their curves are similar in 

 nature to that of the liver-fed albinos. 



To what factor or factors is due, 1) the normal growth rate 

 of the albinous larvae supplied with fresh anterior lobe and 

 the hypophysial residues, and, 2) the retardation of specimens 

 fed with liver, hypophysial extractives, and colloid? The nor- 

 mality of the growth rate exhibited by the specimens of the first 

 division might conceivably be due to the superior nutritive 

 value of the anterior lobe rather than to a morphogenic agent. 

 If this was the responsible factor, however, we should expect as 

 great a deviation in both the magnitude and the nature of the 

 growth curves of normal tadpoles fed in this way. No such 



^1 It is to be noted, however, that the normal specimens received a diet of fresh 

 anterior lobe, not of liver. A slight acceleration in the normal produced by this 

 diet may account for the divergence in the two curves. 



