524 W. W. SWINGLE 



Morse fed desiccated thyroid gland to the larvae of Rana 

 pipiens and obtained the same results as Gudernatsch. This 

 investigator also obtained positive results by feeding iodised 

 blood albumin, but was unable to produce results with various 

 inorganic iodine compounds. The gonads were not examined. 



Lenhart found that the higher the iodine content of the gland 

 fed to the larvae, the more rapid the body metabolism. This 

 observer also found that the thyroid effect is inhibited in tad- 

 poles by cold, or by feeding cracker crumbs. 



West fed thyroid tablets to the larvae of Rana catesbiana and 

 found that metamorphosis was greatly accelerated. 



Barthelmez also fed thyroid to the larvae of various amphibians 

 and obtained positive results, the larvae undergoing meta- 

 morphosis more rapidly. 



MATERIAL AND OBSERVATIONS 



The following experiment began April 20, 1915, and continued 

 until June 1, 1916. The larvae of three species of frogs were 

 used in the work: Rana pipiens, Rana catesbiana, and an 

 undetermined species of the same genus. I shall devote the 

 first portion of this paper to a discussion of the work done in 1915. 



April 7, 1915, the eggs of Rana pipiens were gathered from a 

 string of shallow pools near the University campus at Lawrence, 

 Kansas, and brought to the laboratory to develop. Most of the 

 eggs were in fairly late segmentation stages and some had de- 

 veloped to the stage of body elongation. When the mouth had 

 formed and the larvae were capable of feeding, one hundred of 

 the tadpoles were selected and divided into two lots of fifty 

 tadpoles each; one lot to serve as controls for the other, which 

 was intended for thyroid feeding purposes. Each group of 

 animals was placed in a large glass fish bowl, 25 inches in cir- 

 cumference by 12 inches deep. Ordinary tap water was used 

 to cover the larvae and was changed daily. Both cultures of 

 tadpoles were kept under uniform conditions of temperature, light 

 and water supply. The larvae of both series of tadpoles aver- 

 aged the same in length when the experiment began, that is 10 

 mm. A convenient method of measuring the animals is to lav 



