362 EXPERIMENTAL GIGANTISM 



DISCUSSION. 



The feeding of anterior lobe to metamorphosed salamanders has 

 two different effects on the growth of the animals: first, it increases 

 the rate of growth over that of normal animals; and, second, it main- 

 tains growth after the normal "maximum" size of the species has been 

 attained. Have we any reason to consider these eJBfects as the result 

 of a "specific" growth-promoting hormone? 



As to the first point, we cannot be quite certain that the rate of 

 growth of our control salamanders was the highest rate of growth 

 which can be obtained with a normal diet. Unfortunately the data 

 available on the growth of metamorphosed salamanders are not 

 numerous enough to decide if earthworms form a sufficiently complete 

 diet for the two species in question. Although it is quite certain 

 that these animals do not require a plant diet, not enough food mate- 

 rials have been tested by the writer to state on which food they nat- 



The two largest hypophysis-fed specimens of Aniby stoma opacum exceed in 

 size the largest known animal of this species by 19 and 11 mm. respectively. 



Ambystoma ligrinum. 

 Eastern race. 



Among the five hjrpophysis-fed specimens of Ambystoma tigrinum three are 

 considerably larger than the largest known specimens of the eastern race, the 

 largest hypophysis-fed specimen exceeding in size the largest eastern specimen 

 by 28.5 mm. 



There is, as stated above, a western giant race of Ambystoma tigrinum. Dr. 

 Stejneger gives 258, 265, 285, 285, and 292 mm. as measurements of the five 

 largest specimens of this race. The largest of our hypophysis-fed animals, which 

 has grown 5.5 mm. in the last 4 weeks and measures at the time of writing 273.5 

 mm., has already outgrown two of the western giants and will soon outgrow the 

 three others if it continues to grow at the present rate. 



