CADUCIBRANCHIATA. 53 



ANIMALS KNOWN ONLY IN THE LARVAL 

 STATE. 



While the following species have hitherto been refer- 

 red to a distinct genus, the researches of Dumeril, Marsh, 

 and Tegetmeier render it probable that they are only 

 immature forms, and probably as suggested by Cope in 

 regard to the first, they all belong to the genus Amblys- 

 toma. At the same time it should be borne in mind that 

 no one has ever seen a species of true Axolotl, such as 

 Siredon Mexicanus, undergo metamorphosis, all the ob- 

 servations recorded on this point having been with 

 Siredon lichenoides, which soon after naming by Prof. 

 Baird, was suspected of being a larval form. Still fur- 

 ther, in all the collections brought from Mexico not a 

 single Amblystoma has ever been obtained south of the 

 26th parallel, while the Axolotl inhabits the Lake of 

 Mexico. Dumeril has also shown that the Siredons 

 were capable of reproduction, while so far as our pres- 

 ent knowledge goes, the metamorphosed Amblystoma 

 is always barren. These facts leave still room for doubt 

 as to whether these animals undergo transformation. 

 And yet while no specimen has ever been observed show- 

 ing a tendency to a change, their relation to an animal on 

 which observations have been made is such as to render 



