98 ON THE STRUCTURES AND DISTRIBUTION OF THE 



as to indicate at once their pertinence to widely different groups ; and in the case of 

 Siredon, an identity with a Isnown series of the Caducibranchiates, the Amblysto- 

 mata. This identity is rendered plain in the appended diagnosis. 



In certain species of the genera Spelerpes and Amblystoma,* the branchiae remain 

 to near the adult age, and are the last larval features to disappear. I have frequently 

 seen the apparently adult Amblystoma mavortium with considerable stumps of 

 the branchiae remaining, and even a few fimbriaB. The abundance and size of the 

 larva3 of Spelerpes salmoneus, and rarity of the adults, have been pointed out by 

 Prof Baird,t who also has recorded his belief in the great probability of the Siredon 

 pisciformis being the larva of some unknown Amblystoma. The latter creatures 

 are known to lay eggs, and hence the probability of their being adults, and not 

 larvae. In another species with completely developed gills and dorsal and caudal fin, 

 brought by Dr. Coues from Arizona, I find largely developed ovaries filled with eggs, 

 some in an advanced stage. Moreover, the carpal and tarsal bones are ossified, al- 

 though cartilaginous in many Urodela, which lose the branchiae. 



The question appears, however, to be finally settled by the remarkable facts ob- 

 served recently at the Jardin des Plantes by Prof A. Dumeril. Siredons laid eggs, 

 which hatched ; the larvae developed into Siredons, and, continuing to change, be- 

 came Amblystomas ! a confirmation of the suspicion of Prof Baird. The character 

 is in this case not even specific. 



The position and tissue of the external branchife render them liable to injury; 

 the following illustrates how little such injury affects the vitality of the individual : 

 Dr. Coues states that his Siredons were taken in a well, by a baited hook. They 

 were laid in the scorching sun, and remained there nearly an hour before being carried 

 awaj' and placed in water. They recovered perfectly; the skin exuded moisture 

 during their exposure to the heat. The gills were hlaclc in this species, in life. 



Some years ago I had occasion to observe a Siren confined in an aquarium, which 

 had been taken near Alton, 111. (Lat. 39°). I first saw it in midwinter; it was then 

 without gills, but frequently came to the surface and took mouthfuls of air, parts of 

 which would escape through the slits on the neck. There were frequently convulsive 

 movements of the latter region, by which the anterior and sometimes the posterior 

 slits were opened. Water was at the same time drawn in through the external nares, 

 and probably reached the pharyngeal cavity. The animal was said to have suffered an 

 absorption of the gills, which lasted two weeks, during which time it would take no 



* In Amblystoma punctatum and opacum the branchiae disappear while the animal is but half its 

 future size : the period at which they disappear in Desmognathus f u s c a appears to vary, but averages as the 

 preceding ; in Hemidactylium scutatum and Geotriton carbonarius their absorption takes place while 

 the animal is very small. In Plethodon erythronotus they also remain a very short time and are of no 

 functional value, as the larva does not enter the water after leaving the egg. 



t Jour. Acad. Nat. Sci. Philada., i. p. 281. 



