^ BIOLOGY. 315 



salamander, a conclusion stren<:^thenecl by similar changes noticed 

 in the Siredon from the Rocky Mountains, by Prof. Marsh. 



The first phase observed in the transformation was the appear- 

 ance of dark spots on the sides of tlie tail, and, soon after, the 

 membrane along the back, and especially that below the tail, 

 began to disappear by absorption. Next the external branchiae 

 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 

 branchise, as well as the branchial arches, became absorbed, and 

 the openings on the neck closed by the adhesion of the opercular 

 flap. The body diminished in size ; the head became more rounded 

 above, and more oval in outline ; the eyes became more convex 

 and prominent, the opening of the mouth larger, and the tongue 

 considerably increased in size. Important changes also took place 

 in the teeth and in other parts of the structure, and the animal 

 finally escaped from the water a true Amblystoma, not to be dis- 

 tinguished from A. mavortium (Baird). Subsequently, several other 

 siredons went through tiie same metamorphosis, during which it 

 was shown that the rapidity of the change was greatly affected by 

 variations in light and temperature, the specimens most favorably 

 situated in these respects having undergone apparently their en- 

 tire transformation in about three weeks. "Whether the species 

 ever changes in its native lake, about 7,000 feet above the sea, is 

 uncertain, but it probably breeds in the siredon state, like the ax- 

 olotls from Mexico. This interesting metamorphosis leads to the 

 suspicion that other so-called perennibranchiates may prove to ])e 

 the undeveloped j'oung of well-known species. — Proceedings Bos- 

 ton Society Natural History, Sept., 1868. 



The menobranchus of Lake Superior, kept for two years under 

 the most favorable conditions as to light, temperature, and food, 

 did not undergo any of the above changes ; nor is there in the 

 north any salamandroid of sufficient size to be regarded as the 

 possible adult condition of the menobranchus. — Editor. 



DISCOLORATION OF THE SEA. 



Arctic voyagers have long been familiar with the *' black water" 

 of Davis's Straits, Baffin's Bay, and other northern seas, in which 

 the color is dark olive-green or even black. This color has been 

 generally attributed to the presence of great multitudes of minute 

 animals, as medusae, entomostracan crustaceans, and pteropods. 

 It was noticed, however, by Mr. Robert Brown that, though these 

 animals often sunk, the water still retained its dark color. He 

 afterward discovered the cause to be great numbers of diatoms, 

 chiefly of one moniliform species, of undetermined name. The 

 medusas and other animals feed upon these plants and are them- 

 selves the food of the whales which frequent these waters. The 

 same diatoms are the cause of the brown "rotten ice" of the 

 polar regions. 



The yellowish-brown scum, called by sailors " sea-dust," seen 



