M. F. Plateau on the Aquatic Articulata. 365 



sea-water does not explain the death of the freshwater Articu- 

 lata in the latter liquid. 



Resuming tl^e experiments indicated by me in a former 

 memoir, I exposed some Articulata on which I had ascer- 

 tained that sea-water has an injm'ious action to a solution of 

 cane-sugar in water, brought, by means of Fahrenheit's areo- 

 meter, to precisely the density of the water of the ocean. Out 

 of eleven species eight lived Avith impunity in the solution of 

 sugar ; and with the others the action was much slower than 

 tliat of sea-water or of the chlorides. 



6. When the freshwater Articulata pass, by a very slow 

 transition, from fresh to sea-water,' and reproduction has taken 

 place during this transition, the new generation resists the 

 action of sea-water longer than the ordinary individuals of the 

 species. 



The exposition of this experiment would occupy more space 

 than is desirable in a simple abstract ; I shall therefore take 

 the liberty of referring the reader for its details to my memoir. 



I slowly modified the fresh water in which a great number 

 of specimens of Asellus aquaticus were living, in such a man- 

 ner as to transform it in the course of two months into natural 

 sea-water, taking all the precautions necessary to keep the 

 water sweet and to provide the Crustaceans with nourishment. 

 During these two months (from the 21st January to the 16th 

 March) the AseJU reproduced. 



The result of the experimeftt Avas, not a modification of the 

 original individuals, as these gradually died out, and none re- 

 mained on the 3rd March, but a modification of their descen- 

 dants, Avhicli almost rendered them a new variety, as to their 

 aptitude for living in sea-water. In fact, under ordinary con- 

 ditions the AseUi do not resist the action of sea-water, at the 

 maximum, more than 5 hours 15 minutes, and the young die 

 more quickly than the adults in this liquid, whilst seven of the 

 individuals born during the experiment lived in pure sea- water 

 for 108 hours. 



Marine Crustacea. 



7. The commonest Crustacea of the Belgian coast die in 

 fresh Avater after the lapse of a variable time, which, however, 

 does not exceed 9 hours. 



8. The marine Crustacea Avhcn immei'sed in fresh Avater 

 give up to this the salts (especially chloride of sodium) Avith 

 which their tissues were impregnated. 



If the freshwater Articulata, when immersed in sea-water, 

 absorb certain of its salts, the marine Articulata lose in fresh 

 water the salts contained in the liquids of their bodies. Hence 



Ann. d; Mag. N. Hist. Ser. 4. VolVn. 26 



