NOTES. 437 



litcrata, of which I have found identical specimens on Fucus, on the 

 high seas, in brackish water in the estuaries of tne Philippines and in 

 pure fresh water high up the country in Luzon; it also lives in Lake 

 Taal. Three or four still undescrifced species of the marine form 

 Hymenosoma 1 discovered in the bogs and rivers of the Philippines and 

 in the river near Canton. Sirgvs, CenoUta, many Oraj)soidce, Oecarcinus 

 and others — Crustaceans living on land — properly speaking do not 

 belong here, but they may be mentioned, for at least they do not live in 

 sea-water and are certainly often enough exposed to rain. 



A species of Pchubus lives in a tributary of the Sutlej at the foot of 

 the Himalayas (Huxley, P?'oc. Zool. Soc. 1878, p. 787). Penaus hradUendi 

 goes high up the rivers of North America. (Baird. i?e/;. on Fisheries, 

 1872.) 



Mollusca. 



No marine mollusca living in fresh water, besides those named in 

 the text, are known to me ; perhaps, however, Teredo senegalensis 

 (Blainv.) may be added. Aucapitaine's statement, that Cypr(ea moneta 

 is found in the waters of the interior of Sudan and caught by the 

 natives with calf's hides, has been disputed, but Aucapitaine repeatedly 

 maintained the truth of his assertion. It does not appear, however, to 

 have been confirmed by later travellers. 



VcrtcTirata. 



■ Many migratory marine fishes might be added to the list given in 

 the text ; for instance, the species of Shad, many Pleuronectes and 

 allied forms — a flounder occurs as high up as Metz and Treves (Trier) 

 according to Leuthner. Cat-fish and the well-known Manatus live 

 in the rivers of S. America (the Indian sea-cow — Halioore — the nearest 

 ally of the Manatus— is found only in the sea) with numerous other 

 fishes whose nearest congeners are typically marine, such as a species 

 of Biodon. In the eastern hemisphere several species of the genus 

 Hemirliamplms live in fresh water which are only specifically distinct 

 from their marine allies. 



Note59,]>age 151. According to Bernard's researches on the frog 

 and Plateau's on Crustacea, we might almost be tempted to suppose 

 that in all animals that migrate from the sea to rivers, and lice versd, 

 the different degree of saltness between their tissues and the surround- 

 ing water would be rapidly equalised by the osmotic action of the skin. 

 In many creatures, as, e.g., the Stickleback, this is no doubt the case — 

 though no conclusive experiments have been made even on this fish ; 

 in others, as the Crocodile, it may be doubted whether even in indi- 

 viduals actually living in the sea the flesh would be salt. No exact 

 investigations exist. From the easily observed fact that a fresh-water 

 stickleback when suddenly transferred to salt water cannot at first 



