6io Studies in the Theory of Descent. 



justified in striking out the genus Siredon and in 

 placing S. Mexican us as an undeveloped form in 

 the genus Amblystoma. So long as there exists 

 not one only, but several species of Siredon which 

 as such regularly propagate themselves, the genus 

 exists ; and although we would not deprive syste- 

 matists of all hope of these species of Siredon 

 being one day re-elevated to Amblystomce, it never- 

 theless better accords with the actually existing 

 state of affairs if we allow the genus Siredon to 

 remain as before among the genera of Salaman- 

 drina, and to include therein all those species 

 which, like the Paris Axolotl, S. Mexicanus, Shaw, 

 and probably also S. Lichenoides, Baird, only ex- 

 ceptionally, or through artificial influences, assume 

 the Amblystoma form, but without propagating 

 regularly in this condition. On the other hand, we 

 should correctly comprise under the genus Ambly- 

 stoma all those species which propagate in this 

 state regularly, and in which the perennibranchiate 

 stage occurs only as a larval condition. 



To arrive at a decision in single cases would 

 chiefly concern the American naturalists, whose 

 ever increasing activity may lead us to hope soon 

 for a closer investigation of the reproduction of 

 the numerous species of Amblystoma of their 

 native country. I should rejoice if the facts and 

 arguments which I have here offered should give 

 an impetus to such researches. 



The second consequence to which I may refer, 



