ATROPHY OF THE ORGANS OF THE LARVAL FROG. 163 



internal secretion in the thyroid gland, rather than functioning 

 as hormone itself, is untenable. In either case it would clear up 

 the apparent discrepancy in the findings of Voegtlin and Strouse 

 and in those of the students of amphibian metamorphosis. 



THE ECONOMY OF THE PROCESS. 



In the investigations upon the salmon conducted by Miescher 

 and later by Noel Paton and others, it is evident that there is a 

 high degree of economy involved in the process of metamorphosis 

 of the muscles into gonad material. The question arises, is this 

 true for the metamorphosis of the larval frog? 



In the foregoing paragraphs, we have spoken of this process of 

 metamorphosis as if it were confined to the regions of the tail, 

 but the difficulty of studying the participation of the alimentary 

 tract, gills, etc., in the process is not a small one and these inves- 

 tigations have been confined to the changes in the tail. One 

 primary difficulty regarding the study of the alimentary tract 

 is that at metamorphosis, preceding the shortening of that sys- 

 tem, a large accumulation of fecal matter is expelled, containing 

 the same chemical compounds which are utilized in studying the 

 transformations of tissues. It is for this reason that the simple 

 expedient of weighing the organism before and after metamor- 

 phosis to determine the loss, if any, of material, is not feasible, 

 the fecal matter far overbalancing any amount of product of 

 tissue change thrown to the outside. 



A study was made of the excretions of the larvae immediately 

 after the expulsion of the fecal matter. Larvae were isolated in 

 distilled water in large petri dishes. After twelve hours, the 

 water was filtered and estimations were made of the total nit- 

 rogen, amino-nitrogen, ammonia and urea. While the method 

 was crude, owing to the impossibility of inhibiting the transfor- 

 mation of urea into ammonia and of the probable deaminization 

 of the amino-acids by bacteria, there was no constant difference 

 in the figures for non-metamorphosing and metamorphosing 

 lavrae. Unless, then, there were extensive excretion of the 

 products of the decomposition of the larval tissues, it is safe to 

 conclude that the process is an economic one, the tissues of the 

 larval organs contributing to the formation of those of the adult. 



