5 go Studies in the Theory of Descent. 



change occurs, but only a kind of functional 

 change in the sense used by Dohrn. 25 This is the 

 case for example, when Forel 26 shows that fresh 

 water Pulmonifera, the organization of which is 

 attributed to the direct respiration of air, can 

 nevertheless become settled in the greatest depths 

 of mountain lakes through their lungs being again 

 employed as gills. That not the least change in 

 the lungs hereby takes place is shown by the 

 observations of Von Siebold, 27 who saw the shallow 

 water Pulmonifera using their lungs alternately 

 for direct aerial and aquatic respiration, according 

 to the amount of air contained in the water. If 

 with Von Siebold we merely apply the word 

 " adaptation" to such cases, this expression would 

 lose the special sense which it originally conveyed, 

 and the word would have to be abandoned as a 

 terminus technicus ; still, such cases may perhaps 

 be spoken of as physiological adaptation. 



In any case the reproductive " larvae " of the 

 Tritons as little present a case of true adaptation 

 as the Axolotl, which occasionally becomes trans- 

 formed into an Amblystoma. In both cases the 

 transformation referred to is by no means indispen- 

 sable to the life of the individual. Mature Tritons 



** " Der Ursprung der Wirbelthiere und das Princip des 

 Functionswechsels," Liepzig, 1875. 



26 Bull. Soc. Neuchatel. vol. viii. p. 192. . Reference 

 given in "Troschel's Jahresbericht " for 1869. 



17 Sitzungsberichte d. math. phys. Klasse der Akad. d. VViss. 

 zu Miinchen, 1875. Heft i. 



