402 w. w. SWINGLE 
failure (i.e., Jensen's), in particular the fact that the animals 
were too old when they were subjected to the thyroid feeding." 
And elsewhere the same author states "that nothing is known of 
the endocrine system of Proteus." 
The writer ventures to predict that if the thyroid glands of an 
untreated Proteus are engrafted into anuran larvae, the latter 
will react similarly to those engrafted With Necturus glands. 
These experiments negative any such assumption as Uhlenhuth's 
('21, page 201) that, "if the thyroid substance is capable of 
causing the development of the characters of a terrestrial amphib- 
ian, the administration of thyroid substance should cause the 
metamorphosis of Proteus anguineus. " This writer apparently 
holds the View that any perennibranchiate will, if fed thyroid, 
metamorphose, and that retention of larval characters in these 
forms is due to absence or defect of the thyroid mechanism. 
The present experiments lend no support to any such hypothesis. 
In regard to the statement that the endocrine system of Proteus 
is unknown, it is interesting to note that Franz Leydig in 1853 
(p. 62), describes the thyroids of this animal. According to his 
description, they apparently do not differ greatly from those of 
Necturus. 
Uhlenhuth lays great emphasis upon the fact that one of the 
perennibranchiates, Typhlomolge rathbuni, is said to lack the 
thyroid gland, and states in effect that the reason for the retention 
of the larval characters is due to the thyroid absence. Perhaps 
this is true, but it strikes the writer as being rather odd that the 
retention of larval characters of this perennibranchiate should 
depend upon the absence of the thyroid function, and that such 
characters are retained in another form (Necturus) in spite of the 
presence of a most potent and active thyroid, in spite of feeding, 
injecting, and engrafting of thyroid substance. 
There is another point of interest in connection With the dis- 
cussion of Typhlomolge, and that is the apparent absence of 
thyroid glands in adults of this peculiar animal. Emerson ('05) 
studied the general anatomy of two specimens preserved in 4 
per cent formalin, and merely mentions in the course of her dis- 
cussions, "Sections of the head reveal the presence of a thymus 
