194 BENNET M. ALLEN 



with alum-cochineal was then cut into sections 25m in thick- 

 ness. These were searched most carefully for any e\'idence of 

 thymus tissue, but no traces were found. In the other speci- 

 mens the two sides of the head were cut away in such fashion as 

 to include liberally the thymus region and parts near it. These 

 were stained in toto, cleared, and examined in oil of wintergreen. 

 Reliance could hardly be placed in this method, so they were 

 later imbedded and cut into sections for further examination, 

 every section being critically studied. By these laborious means 

 it was possible to check up the accuracy of the operation in each 

 specimen. It may be said with certainty that there w^ere no ves- 

 tiges ever so slight of the thymus glands in any of these cases. 

 In nos. 12 and 13 only one thymus gland was in each case pres- 

 ent, while in no. 14, a specimen that had been operated upon, 

 both were found to be intact. Controls nos. 15 to 32 were reared 

 under conditions like those of the thymusless specimens, while 

 nos. 33 to 50 were purchased from a dealer. They had been 

 preserved in formalin. Naturally, they are not as satisfactory 

 as a check upon these results as are the other controls. 



RESULTS 



This work is most important in the fact that it is the first 

 series of experiments in which the thymus glands were removed at 

 their very ince]:>tion. Experiments upon mature and even upon 

 young animals lose much of their significance because they do 

 not touch upon the important period of early development when 

 the glands would be expected to exercise their greatest influence 

 upon growth. While Adler ('14) operated upon earlier stages 

 than had formerly been employed, the thymus glands had reached 

 a high degree of development at the stage at which he operated, 

 and had presumably been exerting their influence for some time, 

 if they really function as endocrine glands at all. It is perfectly 

 safe to conclude from my own experiments as well as from Ad- 

 ler' s that the thymus glands exert no influence upon metamor- 

 phosis. It is also clear that they do not exert any appreciable 

 influence upon growth in size. Attention has often been called 

 to the interrelations in tlie mammals between the thymus glands 



