362 M. F. Plateau on the Aquatic Articitlata. 



Protozoa. 

 CUone celata^ Grant. R. & C. C. 



Plant.e. 

 Conifer^ sp. R. C. Waldrlngfield. 



XL VI. — Physico-chemical Investigations uj)on the Aquatic 

 Articulata. By Felix Plateau. Part I.* 



This first part includes the investigation of the phenomena 

 presented by the aquatic Articulata (Insects, Arachnida, and 

 Crustacea) when placed in liquids the saline composition of 

 which is not the same as that of the waters in which they 

 habitually live. In the present memoir I have left out of 

 consideration mineral waters properly so called, as their ex- 

 tremely varied composition would have necessitated a consider- 

 able number of experiments the results of which would have 

 been of little use. 



The influence of sea-water, or of salt water, upon the Arti- 

 culata which usually inhabit fresh water, and that of fresh 

 water upon the marine Articulata, on the contrary, possessed 

 some real scientific interest. We have long known several 

 species of fish which are able to live indifferently in both 

 liquids, and we also know that there are Crustacea and beetles 

 endowed with the same faculty. But, side by side with these 

 few exceptions, what an enormous quantity of aquatic species 

 which always seek the same water and the same conditions, 

 and to which the least modification seems to be injm'ious ! 

 Why should the carnivorous larvaj of the fresh waters have a 

 repugnance to exchange their ordinary fare for species of 

 My sis ^ Slabberina, and Cetochilus^ or even young marine fishes ? 

 What is the cause that prevents many marine Crustacea from 

 ascending the rivers by the aid of the tide, and taking up their 

 abode in waters rich in living prey, and where, by their 

 strength and the hardness of their integuments, they would 

 soon reign as masters ? 



The very nature of the experimental researches to which 

 these reflections have led me renders a summary exposition of 

 them very difficult. As it is impossible here to reproduce the 

 tables containing the results of numerous experiments, I shall 

 confine myself to the enunciation of the various conclusions at 

 which I have arrived, following these, if there is occasion, with 

 some observations or with a few examples. 



* Abstract of a Memoir in the ' Memoires de rAcad^niie Royale de 

 Belgique,' 1870. Communicated by the Author. 



