Functional and Ontogenetic Stimuli Alike 307 



add further the following more special ones which are 

 quite similar in their nature to the preceding. 



The tails of larval amphibians, cut off obliquely in 

 respect to their axes, become regenerated in such a way 

 that the axis of the regenerated fragment is always per- 

 pendicular to the plane of section and forms consequently 

 a certain angle with the axis of the stump. Nevertheless, 

 all these tails, because of regulative forces within the 

 organism, tend gradually to straighten themselves. Now 

 Barfurth has demonstrated that in frog larvae which are 

 prevented almost entirely from swimming by putting" 

 them in shallow water divided into a number of small 

 compartments by water plants, this straightening goes on 

 in a much less complete manner and much more slowly 

 than in those which are placed in deep w r ater and which 

 are thus able to swim freely. That is a proof that func- 

 tional adaptation of the tail to swimming co-operates with 

 the entire action of the internal regulative capacity, or in 

 a wider sense with the ontogenetic stimuli, and adds it- 

 self to them, intensifying and accelerating their action. 226 



An example of the ontogenetic stimulus having not 

 yet replaced the functional, or better, being not yet 

 endowed with a quantity of potential energy sufficient to 

 overcome by itself the resistance which opposes its acti- 

 vation, and which has therefore need of this functional 

 stimulus in order to commence to act, is furnished us 

 by the axolotls. These tailed batrachians can retain 

 their external gills indefinitely and live out their lives 

 and reproduce their kind with external gills, or be trans- 

 formed into amblystomae, according as they are or are 



228 Barfurth : Versuche zur funktionellen Anpassung. Arch. f. 

 mikrosk. Anatomic, Bd. XXXVII ; Drittes Heft. Bonn, Cohen 1891 ; 

 especially P. 403 405. 



