202 BENNET M. ALLEN 



caused a hypertrophy of the parathyroid glands to twice their 

 normal size. He reports gland-like hollows containing colloid 

 in the parathyroid glands of normal animals, but finds them to 

 be far more numerous in cases where the thyroid gland has been 

 removed. A number of writers have described a hypertrophy of 

 the thyroid glands in cases where the parathyroid glands have 

 been removed. 



In the spring of 1918, the thyroid glands of Bufo were removed 

 in the manner described in an earlier paper (Allen, '18). These 

 tadpoles failed to metamorphose, as had been previously demon- 

 strated. They were killed at various ages after having lived long 

 beyond the period of normal metamorphosis and having reached 

 gigantic size; they were for the most part, preserved in bichro- 

 mate-acetic fluid. The more advanced young toads were fixed 

 in 5 per cent formalin. The region of the thjToid and parathy- 

 roid glands was sectioned at a thickness of 10 m, after staining in 

 toto with alum cochineal. The controls used included speci- 

 mens killed before, during, and after metamorphosis. 



In the anurans the parathyi-oid bodies, four in number, are 

 quite distinct from the thyi'oid glands and in close association 

 with the aortic arches. They were measured by counting the 

 number of sections through which each extended and by taking 

 measurements in two dimensions upon the largest section of 

 each. In each case an average of each dimension was taken for 

 the four parathyroids of every specimen. The three average di- 

 mensions were then multiplied together to give the volume of a 

 parallelopiped that would thus contain a parathyroid gland of 

 average size. By such an approximation of volume it is possible 

 to have a basis of comparison for the parathjToid glands of 

 different specimens. 



There is a large amount of variation in the average volume of 

 the parathyi'oid glands in different specimens. It is difficult to 

 account fully for this. \^Tiile there are certain exceptional cases, 

 as nos. 1, 6, and 11 among the controls and 26 among the 

 thyroidless specimens, there is generally a certain amount of 

 regularity in average size. While metamorphosis causes an ap- 

 preciable diminution in body size and a decrease in the volume of 



