ANATOMY AND PHYSIOLOGY OF ATRINA RIGIDA. 
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currents sweeping anteriorly in the ventral part of the mantle chamber, turning dorsally 
between and over the outer surface of the gills. The inflow of the water seems to be 
due in part to the action of the fine cilia of the inner surface of the mantle, but the gills, 
much of whose inner and outer surfaces are ciliated, are evidently the seat of the great 
pulling force. 
FOOD-BEARING CURRENTS. 
The respiratory current entering the mantle chamber carries with it many small 
objects in suspension, including minute living organisms. These are not allowed to pass 
through the gills, but are filtered out and passed in slow moving currents toward the 
mouth. These food-bearing currents are easily followed when powdered carmine, sus- 
pended in water, is dropped upon the gills. The particles of carmine are seen to move 
outward to the free border of the gill, where they enter the longitudinal groove in its 
edge and pass toward the anterior, finally reaching the palps, between which they con- 
tinue to the mouth. These respiratory currents and food-bearing currents have long 
been known, and they seem to be much the same in all lamellibranchs. It was thought 
until recently that so long as water was flowing into the mantle chamber the lamelli- 
branch had no choice but to receive the food, strained from it, into its digestive tract. 
In 1900 J. T. Kellogg (7) showed that when food was not desired it could be turned aside 
in the palps and deposited by them into backward-moving currents in the mantle, 
through which it was carried directly or indirectly to the exterior. Stenta (14), working 
independently upon many forms, including Pinna, came to the same conclusions. In 
Atrina I found the food-bearing currents turned aside at about the middle point of the 
palps at the anterior end of the corrugated portion. Here it moves outward to the edge 
of the palps and then posteriorly to their tips, where it leaves them to enter the ciliated 
canal of the mantle, which transports it to the exterior. Whether lamellibranchs can 
exercise choice in their food, accepting only the part which is desirable, is not known. 
C. Grave (3) compared the contents of the digestive tract of oysters with diatoms found 
in the water above their beds and came to the conclusion that they have the ability to 
choose. J. L. Kellogg read a paper before the American Society of Zoologists in Decem- 
ber, 1909, in which he stated that it is not the nature of the food but the quantity of it 
which causes lamellibranchs at times to reject it. When great quantities of food 
material are carried to the palps by the gills they reject it. In this case it passes out- 
ward in the grooves of the corrugated portion of the palps to their outer borders and then 
posteriorly to their tips. It then enters the backward-moving currents in the mantle 
chamber and is expelled. 
CIRCULATORY SYSTEM. 
In order to get a good injection of the blood vessels it was necessary to narcotize 
the specimens. Otherwise they would contract to such an extent as to make the rela- 
tion of the parts unintelligible. This was done by placing them in a large pan of sea 
water and adding alcohol slowly until dead, which required from six to eight hours. By 
this means they remained expanded and the vessels were relaxed sufficiently to allow 
easy penetration of the injecting fluid. 
