EDUARD UHLENHUTH 543 



been shown to be actually the case for metamorphosis and coloration 

 in Aniby stoma tigrinum, and probably the same cause is responsible 

 for the production of metamorphosed animals without tongue and 

 with a larval arch of palatal teeth. 



It is probable that two factors are causing metamorphosis, iodine 

 and excretor substance. A third factor is probably involved in in- 

 hibition of metamorphosis at low temperature; namely, a change of 

 the thyroid gland, making this organ progressively less susceptible 

 to the excretor action, with progressing age. The inhibition of the 

 development of the yellow bands at low temperature in the species 

 Amby stoma tigrinum is so similar to the inhibition of metamorphosis 

 by low temperature in the same species as to suggest that the mech- 

 anism causing this coloration is composed also of a number of factors 

 interrelated in a way similar to that of the factors for metamorphosis. 

 It would be interesting to find out whether one of these factors, as in 

 metamorphosis, is an internal secretion. 



The experiments reported here show that the independent develop- 

 ment of the germ cells cannot be used to postulate an independent posi- 

 tion of the germ plasma as compared with the somatic plasma, since 

 other groups of organs which so far as known are not composed of 

 germ plasma behave like the germ cells. The fact that in sala- 

 manders different groups of organs are evolved by the action of dif- 

 ferent substances seems to agree well with similar phenomena in plants, 

 since it has been shown that the different organs of the plant are 

 caused to develop separately and apparently without the control of 

 what may be called an organic individuality, by the action of dif- 

 ferent substances, special substances, for instance, serving for devel- 

 opment of leaves and roots. ^^ 



SUMMARY. 



1. The difference in time existing between the first shedding of the 

 skin and the reduction of the gills to mere stubs without fringes is 

 constant and unchangeable, which indicates that the fundamental 

 cause for both is a common one. 



2. This common cause is the action of iodine, and consequently 

 both phenomena constitute, or at least are part of, the metamor- 

 phosis of the salamanders. 



18 Loeb, J., Bot. Gaz., 1915, Ix, 249; 1916, Ixii, 293; 1917, Ixiii, 25. 



