288 EDUARD UHLENHUTH 



normal diet (earthworms). Both series were kept in daylight 

 and at relatively high temperatures — up to 30°C- Many of the 

 animals metamorphosed and developed the yellow spots. All 

 individuals of the thymus-set, without exception showed entirely 

 orange yellow, extremely dense spots, no matter how large or 

 how numerous the spots were. Among the worm-fed animals 

 there was a wider variation in regard to the color and density 

 of the spots — from a relatively light yellow and dense type to a 

 very intense yellow ('almost orange yellow') and very dense type; 

 but there w T as not one individual whose spots were nearly like 

 those of the thymus-animals, (i.e., nearly so reddish yellow and 

 so dense), and this in spite of the fact that all individuals of 

 both sets were the offsprings of one female. The difference 

 in the color was so striking that anyone could have picked out 

 without hesitation the Thymus animals had they been mixed up 

 with the worm-animals. Hence there is a means to change that 

 structure which we thought — from our grafting experiments — 

 to be specific. 



From this it seems to me that we cannot refer specificity to 

 an individual or to a certain group of individuals, but that we 

 must refer specificity of a certain type to the methods which we 

 employ in trying to change the type. If our method is unfit 

 to change it, the type appears to be specific; if our method is 

 able to change it, the type seems non-specific. Of course, in 

 this way, we should agree that specificity is only relative and 

 classifying, but not absolute and not real. 



V. SUMMARY 



1. From a larva of Amblystoma punctatum, each of the two 

 halves of the skin of the head, including one eye, was grafted to 

 another larva of the same species. The animal, from which the 

 grafts were taken, was killed ; the two animals to which the pieces 

 of skin had been grafted, constituted one experimental pair. 



2. In each pair, the appearance of the color characteristics of 

 the adult Amblystoma punctatum skin (network and yellow 

 spots) in the two hosts and in the two grafts, was recorded and 

 these dates were compared with each other. 



