146 EDUARD UHLENHUTH. 



bones were not exposed to any function, the tibiae after a certain 

 length of time assumed their normal shape and structure, but 

 only if they were supplied with nourishment in a proper way, 

 and if sufficient space was left for them to regenerate the missing 

 part. 



The same is true of the tendons. H. Triepel 1 showed that 

 the tendo Achillis of a cat can regenerate only tendon tissue, 

 irrespective of the presence or absence of functional stimuli. 



Our own experiments now prove the same principle also in 

 the case of the eye of Salamandra maculosa; this organ regener- 

 ates its functional structures in the absence of functional stimulus, 

 and furthermore it retains its structure permanently, despite 

 the permanent absence of functional stimulus. For a long time 

 it was believed that a bone only regenerated a structureless 

 mass of callus in the absence of function, and according to this 

 theory it would be assumed that an eye if once degenerated 

 would in the absence of light regenerate undifferentiated 

 retina cells, such as we find in the normal Proteus eye. Never- 

 theless, both eye and bone regenerate the normal and fully 

 differentiated structure, even in the absence of functional 

 stimulus. 



We have seen that in my experiments the velocity of the proc- 

 cess of regeneration was not influenced by function; and even 

 if this had been the case it could not be used as a proof in favor 

 of functional adaptation. There are a number of well known 

 morphogenetic processes, the rapidity of which can be acceler- 

 ated by light, although light bears no relation to the function 

 of the developing organ, that is to say, is not a functional stimu- 

 lus. The most striking experiments made in this connection 

 are those of J. Loeb, 2 in which he showed that the regeneration 

 of the hydrants of Eudendrium is impossible in the absence of 

 light. Nevertheless, we cannot call this a case of functional 

 adaptation, because here light is obviously not a functional 

 stimulus. On the other hand, development of the eyes of 

 fish embryos cannot be prevented by the exclusion of the func- 



1 Triepel, H., "Selbststandige Neubildung einer Achillessehne," Arch. f. Ent- 

 wcklungsm., Aug., 1913, XXXVII., 278. 



2 Loeb, J., "Uber den Einfluss des Lichtes auf die Organbildung bei Tieren," 

 Pflilgers Arch., April, 1896, LXIII., 273. 



