798 KEPOET OF COMMLSSIONEE OF FISH AND FISHERIES. [SJ 



This diatom presents a singular x)ecnliarity, first observed by M. de 

 Br^bisson, as we have already seen from the note cited from M. Petit, 



Fig. 1. 



but which has not yet apparently been published by that savant. We 

 know that the frustule of a diatom is a cell, the silicious wall of which 

 incloses a yellowish pigment (diatomine), disposed, according to the 

 germs, in the form of bands or granules, and a colorless liquid which 

 fills up the rest of the cavity of the cell. For this reason when diatoms 

 of the usual type are examined in mass they have a more or less in- 

 tense yellowish brown color, but this is not the case with N'avicula 

 ostrearia. The two bands of chlorophylloid substance (diatomine) exist 

 in this just as in all other Navimdw, and they are of the usual yel- 

 lowish color, but, aside from them, the intra cellular liquid, instead of 

 being colorless, has a beautiful azure blue tint. 



This tint is more pronounced at the extremities of the frustules than 

 in the middle portion, where it is sometimes entirely absent. This sub- 

 stance belongs to the group of pigments, which are soluble in water, and 

 is different from chlorophyll and diatomine, which do not dissolve in that 

 liquid. Treated with water acidulated with acetic or hydrochloric acid, 

 Navicula ostrearia immediately loses its blue color and the liquid ab- 

 sorbs the latter, becoming bluish-green. When dried this diatom also 

 loses its color. 



These facts being determined, the next experiment to be tried was 

 plainly indicated. What result would we get if we took some white- 

 fleshed oysters and fed them exclusively upon Navicula ostrearia f This 

 we sought to determine in the following manner : Along the edges of a 

 claire, which had become green, we very carefully collected with a spoon 

 some of the green material with which the sides and bottom of the claire 

 was coated. The material so collected in bottles was shaken for an in- 

 stant so as to separate the heavy particles, and the dirt (which is almost 

 impossible to get rid of entirely), is deposited on the bottom of the vessel ; 

 afterwards we i)oured offaud saved the supernatant-colored liquid, which 

 then contained nothing but the diatoms with the admixture of scarcely 

 any foreign matters. We thus also obtained water, which was suffi- 

 ciently charged with the necessary namculm. This operation requires 

 some attention and some dexterity. When the diatoms have been 



