42 



Messrs. J. S. Huxley and L. T. Hogben. 



two explanations. Either the thyroid of Siren is no longer producing the 

 same type of substances as in other Amphibia ; or, if it is continuing to do 

 so, the body of the organism does not respond to the substances produced in 

 the same way as in other species. That this latter is a possibility is shown 

 by the example of Proteus and Necturus, which cannot be transformed 

 by thyroid-feeding. In either event, the large size of the thyroid is very 

 peculiar and demands investigation : possibly it has taken on some new 

 function. From the particulars given by Piatt (1896) it does not appear that 

 the thyroid is under-developed in Kecturus. In Typhlomolge, on the other 

 hand, Emerson (1905) reports the complete absence of a thyroid gland. 

 Leydig (1853) describes the thyroid of Proteus as being small, median, and 

 composed of but 3 to. 15 vesicles, which, however, often contained colloid. 



(e) Exophthalmos Associated with Metamorphosis. 



It is an interesting fact, which, so far as we know, has not been previously 

 emphasised, that Amphibia before metamorphosis have their eyes flush with 

 the surface of their head, but that in the adult state the eyes protrude con- 

 siderably. In the case of the Axolotl the eyes remain flush with the surface 

 so long as the animal remains in the aquatic form, even if it becomes sexually 

 mature. The phenomenon appears to occur equally in Anura and Urodela. 

 In view of the connection of the thyroid with Amphibian metamorphosis, 

 this protrusion of the eyeballs becomes interesting when it is remembered 

 that exophthalmos is one of the most prominent symptoms of Graves's 

 disease. Whether the exophthalmos in Amphibia at metamorphosis has any 

 relation to that of exophthalmic goitre cannot be definitely stated. 



2. Acceleration of Metamorphosis by Iodine with Triton and Salamandra 



Larval. 



Following Swingle's results (1919), a solution of iodine was made by shaking 

 up an excess of iodine crystals in tap- water in a 2-litre flask, allowing to 

 stand for 2 days, and then diluting as required with tap-water. Two larva? 

 of Salamandra maculosa were put into each of a series of dishes containing 

 350 c.c. of fluid each. 



No. 1 was the control (tap-water only), the rest contained a saturated 

 solution of iodine, diluted respectively 10, 50, 100, 500, and 1000 times. 

 The experiment was performed at room temperature in January, 1920. In 

 all except the 1/10 solution the animals fed well. In the control and in the 

 1/100 solution the gill-filaments were unchanged after a week. In the 1/500, 

 the 1/100, and the 1/50 solutions the gill-filaments were somewhat reduced 

 after 5 days. For some reason the greatest reduction occurred in the 



