244 EDUARD UHLENHUTH 



definitely. It always develops while the animal is still in the 

 larval period. Figure 2 pictures the network as it appeared on a 

 larva six months old, kept in a dark room at an average tem- 

 perature of about 15°C. and fed on worms. 



The next stage may begin while the animal is still in the water 

 and under these circumstances indicates that the animal will 

 soon leave the water, or it may begin after the animal has left 

 the water. At any rate, it always begins about this period, 

 and the time of its appearance and further development corre- 

 sponds to the period in which the animal as a whole undergoes 

 those processes which are generally called metamorphosis in the 

 Amphibians. (See Chapter III, p". 251.) For this reason this 

 stage is considered here as 'corresponding with the metamorphosis 

 of the skin. The beginning of this stage is indicated by a general 

 contraction of the network, by means of which it loses its anasta- 

 moses and appears in the form of isolated spots or blots, a phe- 

 nomenon which is — -within the limit of a few days — well defined 

 in respect to time. But the development of the definite yellow 

 spots as they appear on the adult animal, occurs very gradually 

 in most animals requiring about seventeen to twenty-one days 

 and in some exceptional cases much more. After the animal 

 has left the water, all colors soon appear quite dim in conse- 

 quence of the development of relatively dry and dull layers of 

 horney cells lying on the surface of the skin and unshed for a 

 long time. During this period, the spots decrease in size and 

 change their shape, assuming a round form in the majority of 

 animals. Many spots disappear. This stage was called "Separa- 

 tion of the network." Unfortunately no photograph was 

 taken of a worm-fed larva entering this stage. In its place a 

 photograph of a thymus-fed animal kept at a temperature of 

 about 25°C. is shown here (fig. 3) ; it was taken a short time after 

 the separation of the network had started. Although there are 

 certain differences between the color of thymus-fed and worm- 

 fed animals, the stages of development show the same essential 

 features in both cases. The day before this animal was photo- 

 graphed, 102 yellow spots were counted on the right side of the 



