28 SUPER-ORGANIC EVOLUTION 



curiosity among naturalists. This animal had been 

 known for some time, and in late years they were 

 produced in the Jardin des Plantes of Paris. Like 

 the triton, this animal has also external gills, but it 

 retains them during its life like other gill-breathers. 

 The axolotl generally lives and propagates in the 

 water, but suddenly a hundred of these animals in 

 the Jardin des Plantes came forth from the water 

 and lost their gills, so that they were indistinguish- 

 able from the tadpole without gills of North 

 America (Amblyostomd), and thenceforward they 

 breathed by their lungs. In such interesting cases 

 one can see the sudden transformation made by an 

 animal of aquatic respiration on its conversion into 

 an animal of aerial respiration. This rapid transition 

 is also seen in the larvae of frogs and salamanders ; 

 they pass from the condition of an animal Avith gill 

 respiration to that of an amphibious creature with 

 pulmonary respiration. In the same way, the group 

 of frogs and salamanders is seen to be akin to the 

 Siredon in its origin as an animal of gill respiration. 

 Up till now they have remained in this low stage 

 of development. One sees how ontogeny can 

 explain phylogeny, and how the history of individual 

 evolution explains that of the whole group. 1 



While treating of the correlative adaptations, 

 that is to say, the adaptation of an organ necessarily 



1 E. Haeckel, Histoire de la Creation naturelk, p. 214. 



