420 



W. W. SWINGLE 



length and width of twenty thyroid glands of these underfed 

 animals compared with those of iodin-fed and overfed animals 

 is shown in table 2. The measurements given are of the right 

 glands: the left glands were also measured, but as they showed 

 nothing unusual the measurement for them are not recorded in 

 the table. 



TABLE 2 

 Measurements of the thyroid 



It is obvious from these figures that the thyroid glands of 

 iodin-fed larvae are larger than those of normal larvae of the 

 same age and body size (held at 10.5 mm. length by under- 

 feeding), though they are not larger than the glands of normal 

 animals of the same age presenting marked size differences due 

 to overfeeding. As is well known, the thyroids of frog larvae 

 increase in size with the growth of the organism as a whole. When 

 the fact is taken into consideration that the iodin-fed tadpoles 



