1306 BULLETIN OF THE BUREAU OF FISHERIES. 



needle and thread carried through the tissues. The pinch cock (G) is then 

 released on the siphon of the aspirator, which exhausts the air from the vial or 

 tube (D), draws out some of the stomach contents, and causes a slight collapse 

 of the walls of the alimentary canal. The reservoir (A) is then raised until a 

 flow of water is established through the rectum with a resultant slight turgescence 

 of the intestine. There is thus established a current of water running into the 

 rectum, through the intestine, and out of the mouth, carrying with it eventually 

 the entire alimentary contents, which collect in the tube (D) . To facilitate the 

 dislodgment of the more or less impacted faeces, the intestine is occasionally 

 gently tapped with the handle of a scalpel or dissecting needle. With one appa- 

 ratus about six oysters per hour can be opened and operated on, and dissection 

 shows the entire alimentary canal to be freed of contents. The contents of the 

 tube are treated with a few drops of preservative and are concentrated, by pre- 

 cipitation and the removal of the supernatent water, to a standard volume of 

 5 or 10 cubic centimeters, after which the organisms are counted by the Rafter 

 method and the volume calculated as previously described. It is usual to take 

 the average of five specimens as the measure of the food content of a given lot of 

 oysters. 



For studying the rates of feeding of oysters under different environmental 

 conditions, I have recently used the following experimental methods, which have 

 been found effective: 



Pieces of sheet rubber (dentists' "rubber dam ") about 8 inches square, called 

 " aprons, " are prepared by cutting out of the middle semicircular " windows " of 

 about 2 inches radius, over which pieces of no. 25 bolting cloth are cemented 

 with a thick ethereal solution of rubber. A slit about 5 inches long is cut in the 

 rubber parallel to and about ^ inch below the long diameter of the window. 



A number of oysters, about 5 inches long, are then thoroughly scrubbed with 

 a brush, washed in fresh water, the shells covered with a thin layer. of Portland 

 cement so as to fill all cavities and smooth irregularities in their surfaces, and 

 thoroughly dried in the air. 



Each is then inserted in the slit in the middle of an " apron " in such position 

 that the edges of the slit approximate the line running from the dorsal side of 

 the hinge to the point of insertion of the gill at the edge of the mantle. The 

 edges of the slit are then pasted to the shell with rubber solution, care being taken 

 to provide a small fold in the apron at the lip of the shell, to carry it around the 

 dorsal side of the hinge so as not to interfere with the opening of the valves, and 

 to see that there are no gaps between the shell and the rubber at any point. 



Security of adhesion can be promoted by first giving the proper parts of the 

 shell several coats of thin rubber solution, the final cementing being performed 

 with a thick paste made by squeezing the ether-softened crude rubber through 

 cheese cloth and reducing it to the desired consistency by shaking it in ether. 



