OCCURRENCE IN VIRGINIA OF GREEN-GILLED OYSTERS. 1 43 



the organism and at other times it appeared in tiny droplets floating around inside the 

 diatom. The green endochromes, sometimes one and sometimes both, often became 

 twisted and curved out of their normal symmmetrical positions during osmotic changes 

 and gave the diatoms an unbalanced appearance. The nucleus was always centrally 

 located and under normal conditions was surrounded by a mass of transparent proto- 

 plasm. The vacuoles were located at intervals along the length of the organism. 

 Observations on the size of the Navicula osirearia were as follows: Length, 131, 99, 93, 

 andi28niicra; width, 12.8, 9.6, 9.1, and 11. 6 micra. 



The frustules of the Navictda osirearia found in the Chesapeake answer perfectly 

 the descriptions given of the frustules of the Marennes Navicula."' They show a thick and 

 distinct raphe with a valve difficult to distinguish. At a glance they appear smooth 

 without transverse striae, these being scarcely visible. The appearance of the Virginia 

 Navicula osirearia compares exactly with that of the European diatom as set forth in 

 Van Huerck's classification, "A Treatise on the Diatomaceae." 



HISTOLOGY OF THE GREENGILL. 



In order to study the distribution of the green pigment in the gills, histological 

 sections were cut and examined microscopically. The method followed was simply to 

 kill the tissue in HgClj, and then run it up through soft and hard paraffin, cut, and finally 

 stain with differential stains. Haidenhain's hematoxylin and eosin or orange G seemed 

 to answer the purpose very well. It was found that the pigment was locahzed in relatively 

 large, irregularly shaped cells which gave a granular green appearance. These cells did 

 not react to any stain to give a coloring to them but remained green under all conditions. 

 The pigment looked somewhat darker green after staining than it appeared in smears of 

 the gill unstained, but this was probably due to a slight darkening that Haidenhain's 

 had on the pigmented cells or because of the surrounding tissue which was stained very 

 darkly. The location of these cells was in the epitheUal tissue of the gill filaments and 

 along the epitheUum which lined the interlamellar water space, especially in the vicinity 

 of the interlamellar junctions. The appearance and location of these green cells exactly 

 coincides with the description that Lankester gives of his "secretion" cells. 



White gills of Narragansett Bay oysters were studied histologically by the same 

 methods that were used in the greengill study. These showed exactly the same dis- 

 tribution of the large, irregular-shaped cells with granular protoplasm. These, however, 

 were stained by orange G or eosin. The location and appearance of these cells were the 

 same as of the pigmented cells in the greengills. This demonstrated that secretion cells 

 were always present in and on the gills. Lankester said that these cells "furnish pre- 

 cisely the mechanism which we should expect to find in order that the blue pigment 

 absorbed by the blood of the oyster from the contents of the alimentary canal, namely, 

 from ingested Naidcula osirearia, should be deposited at a particular spot on the animal's 

 body. These secretion cells do not occur on other parts of the external surface of the 

 oyster. They are Umited to the surface of the branchiae and to the adoral surface of 

 the labial tentacles." 



This selection and deposit of a pigment in a given tissue has been Ukened, as was 

 formerly mentioned, to the deposition of the red color in the osseous tissue of pigs fed on 

 madder. There is the same analogy found in experiments in which canaries are fed 

 cayenne pepper, a diet which if continued will turn the wings a dark orange color. 



a Dr. Albert Mann has examined some of the material and has confirmed the authors' identification of the Chesai^eake 

 diatom as Navicula osirearia. 



