FUNCTION AND FUNCTIONAL STIMULUS. 143 



proved supply of blood, so that in a comparativey short time 

 (from 4 to 6 weeks) it had regained a perfectly normal structure. 



II. This regeneration of the transplanted eye even takes 

 place when the organ is deprived of functional stimulus by 

 light. A series of salamanders operated on in the above-de- 

 scribed manner, were placed in a dark room where neither red 

 nor white light could penetrate to their eyes; but in spite of this 

 fact the transplanted eyes regenerated and developed a normal 

 retina. 



These experiments show that the "quality" of this process, 

 namely, regeneration as such, is independent of any sort of func- 

 tional influence. We are here dealing with a case of simple 

 regeneration, such as is found in many organs, not with func- 

 tional regeneration, such as we might expect to find in so-called 

 functional structures. Of course this fact does not warrant us 

 in entirely rejecting the theory of functional adaptation, for 

 the possibility must not be ignored that although regeneration 

 occurs in eyes treated in this way as a result of the agency of 

 certain other factors, nevertheless degeneration brought about 

 by atrophy through inactivity might follow later, as a result of 

 the permanent lack of function and functional stimulus, a possi- 

 bility which would be expected to arise according to Roux's 

 theory. 



III. But secondary degeneration as a result of atrophy from 

 inactivity failed to occur in my experiments, even when the 

 eyes were permanently deprived of function, as occurred in the 

 "light" series. 



IV. Degeneration similarly failed to occur in the transplanted 

 eyes which were permanently deprived of both function and 

 functional stimulus, namely in the "dark" series. These eyes, 

 although severed from the brain and in permanent darkness, 

 grew and metamorphosed simultaneously with the normal eyes 

 of the hosts. 1 



Up to the present time I have had at my disposal preparations 

 of eyes of the "dark" series which were preserved 15^ months 

 after transplantation; at that time the hosts were about 21 



1 E. Uhlenhuth, "Die synchrone Metamorphose transplantierter Salamander- 

 augen (Zugleich, Die Transplantation des Amphibienauges II. Mitteil.) Arch, 

 f. Entwcklungsm., April, 1913, XXXVI., 211. 



