THE AMEBIC AN NATURALIST [Vol. L 



ical evidence of the evolution of the true teleosts from 

 ganoid ancestors from the elasmobranchs through forms 

 similar to the sturgeons and the bow-fins. I doubt very 

 much, however, whether ichthyologists would wish to con- 

 clude on this basis that all marine teleosts had their 

 origin from fresh-water forms. In fact certain paleon- 

 tologists trace the evolution of certain fresh-water tele- 

 osts from ancestral marine teleosts. The sea is the home 

 of the preponderating fish population. Here the class of 

 Pisces has found its greatest opportunities for range of 

 movements to escape enemies, in search of food or place 

 of breeding. 



Facts concerning the osmotic pressure of the blood of 

 anadromous fishes throw light as to the possible if not 

 probable origin of fresh-water forms. Greene ( '04) de- 

 termined the osmotic pressure of the chinook salmon in 

 Monterey Bay to be 0.76°. On the spawning grounds in 

 fresh water its blood had a A of 0.628°, a decrease of 17.6 

 per cent. Flatfish are known to be somewhat anadromous. 

 Dakin ('08) found the A of the flounder, Pleuronectes 

 flesus, in the North Sea to be 0.83°, while in the Eiver 

 Elbe in fresh water its blood had a A of 0.68°, a decrease 

 of 18 per cent. The same author found that the blood of 

 the eel, Anguilla, in fresh water had a A of 0.57°, quite 

 similar to that of fresh water fishes. After a day in sea 

 water another specimen had blood with a A of 0.745°. 

 Eels taken from seawater had blood with a a of 0.634°. 

 Eels from seawater placed in fresh water for three days 

 possessed blood with a A of 0.582°, practically the same as 

 for fresh-water forms. At Woods Hole, ignorant of this 

 work of Dakin 's, I made observations on the A of the 

 blood of the white perch, Morone americana. This form 

 can live equally well in salt or fresh water. Taken from 

 the slightly brackish waters of Tashmoo Pond, Marthas 

 Vineyard, Massachusetts, the blood showed a A of 0.635°. 

 The upper end of this pond is the source of drinking 

 water for Oak Bluffs. A number of perch were placed 

 in running tap water for a day, when the blood showed a 



