ISOS. 97 [Marsh. 



September 16, 1868. 



Tlic Presideut in the chair. Twenty-one members present. 



At the request of the President, Prof. O. C. Marsh, of 

 Yale College, gave an account of some observations vvlucli 

 he had recently made on the metamorphosis of Siredon into 

 Aniblystoma, two genera of tailed Batrachia, usually re- 

 garded as belonging to distinct families. 



During an excm'sion to the Rocky Mountains, in August last, Prof. 

 Marsh obtained at Lake Como, a small brackish sheet of water in 

 Wyoming Territory, several specimens of Siredon lichenoides Baird. 

 On bringing them to New Haven, one of them soon began to show 

 indications of a change, similar to that recently noticed by Dumeril 

 in the second generation of the Mexican Axolotls, kept in the 

 Museum d'Histoirc Naturelle in Paris. 



The first phase observed in the transformation was the appearance 

 of dark spots on the sides of the tail, and, soon after, the membrane 

 along the back, and especially that below the tail, began to disappear 

 by absorption. Next the external branchias began to be absorbed, 

 and the animal came more frequently to the surface of the water for 

 air. As the change went on, the spots gradually extended over the 

 rest of the body, the external brauchias, as well as the branchial 

 arches, became absorbed, and the openings on the neck closed by the 

 adhesion of the opercular flap. 



The body also diminished in size; the head changed in form, be- 

 coming more rounded above, and more oval in outUne; and the eyes 

 became more convex and prominent ; the opening of the mouth be- 

 came larger, and the tongue increased considerably in size. Impor- 

 ' tant changes also took place in the teeth, and in other parts of the 

 structure, and finally the animal escaped from the water as a true 

 Amblystoma, not to be distinguished from A. mavortium Baird, 

 according to Prof. Cope's recent definition of the sjaecles. Subse- 

 quently, several other Siredons went through the same metamorphosis, 

 during which, various experiments showed that the rapidity of the 

 change was greatly affected by variations in light and temperature, 

 the specimens most favorably situated in these respects, having under- 

 gone apparently their entire transformation in about three weeks. 

 Wliether the species ever changes in Lake Como, which is about 

 seven thousand feet above the sea, is uncertain, but it probably 



rROCKBDINGS R. S. N. H. — VOL. Xli. 7 OCTOBER, 1868. 



