48 THE ORGANIC GROWTH OF THE LIVING WORLD SEC. 



which in an Axolotl usually occurs only at a more advanced 

 age, and in water but slightly aerated. When the larvae were 

 one year old, the weather continuing warm for some time, a 

 reduction of their gills commenced. Fraiilein von Chauvin 

 gave twenty of the larvae an opportunity to quit the water, 

 and to her surprise some of them immediately crept out into 

 the moss. The metamorphosis began in these after only a 

 few days. One of the larvae completed its change in ten days, 

 and after twenty-three days all the twenty larvae had of their 

 own accord quitted the water. 



Six other Amblystoma larvae of the same brood were kept 

 from the beginning in very cool rapidly-flowing water, and 

 their tendency to breathe air was thus checked, and these 

 remained in the water. 1 



The Amblystoma larvae had therefore inherited the charac- 

 ters acquired by their parents, and the experiments justify 

 the conclusion that in consequence of this inheritance, after 

 a longer duration of the external conditions, the new form 

 Amblystoma would become the permanent species as truly 

 as the perfect spotted Salamander is the species, and not its 

 gill-breathing larva. 



It is supposed that the North American genera Menobran- 

 chus and Menopoma stand in the same relation to one another 

 as Siredon and Amblystoma. 



Further, I may refer to the transformation, shortly to be 

 mentioned, of the crustacean Artemia salina into another 

 species or another genus through the increase or decrease of 

 the saltness of the water in which it lives. Here also a great 

 deal is due to correlative modification. 



On a previous occasion I have endeavoured to describe the 

 physiological causes of this fact of correlation which plays so 

 important a part in the modification of forms, and therewith 

 the ultimate causes of evolution per saltum, in the following 



1 M. v. Chauvin in Zeitschr.fur wissensch. Zoologie, xli., p. 385, 1886. 



