Microns 



150 



Figure 206. — Cross section of the rectum near the anal 

 region. Boiiin, hematoxylin-eosin. 



The rates of discharge of fecal ribbons observed 

 on actively feeding oysters in laboratory sea water 

 of 15.0° to 15.7° C. are given in table 30. The 

 average of the observed rate was 8.1 cm. per hour. 

 Assuming that the average length of the intestines 

 was 12.8 cm., the estimated time of passage of 

 food through the entire alimentary tract was 95 

 minutes. 



The feces of the oyster are voided from the 

 rectum as a compact and slightly flattened ribbon 

 of sufficient consistency to withstand the velocity 

 of the cloacal current. In an actively feeding 

 oyster the ribbon is maintained in a horizontal 

 position along the axis of the current, but being 

 heavier than the sea water it sinks down to the 

 bottom as soon as the cloacal current slows down 

 or ceases. Large masses of fecal ribbons accumu- 

 late on the bottom a short distance from the 

 opening of the cloaca. The ribbon remains intact 

 for 2 to 3 days untU it is disintegrated through 

 decomposition and mechanical disturbance. The 

 appearance of the fecal masses of the oyster is 

 typical and can be recognized by their shape. It 

 was shown by Moore (1931) that specific identi- 

 fication of fecal pellets can be made for a number 

 of marine invertebrates. 



Fecal ribbons of oysters contain many live 

 cells — diatoms, dinoflagellates, yeast, and others 

 which are not killed by the gastric and intestinal 

 juices and can be recultured. 



Table 30. — Rate of formation of fecal ribbons {in cm.) in 

 C. virginica during feeding in laboratory sea water, Woods 

 Hole 



Date 



May 18 

 18 

 18 



May 19 

 19 



May 23 



Rate of 

 formation 



Cm.lhr. 



.7 

 11.3 

 6.8 

 12.2 

 4.6 

 7.2 



DIGESTION 



The digestion and absorption of food in the 

 oyster are primarOy an intracellular process which 

 takes place in the digestive diverticula. This was 

 demonstrated by Yonge (1926a, 1926b) in a series 

 of carefully executed feeding experiinents in which 

 the solutions of iron saccharate, suspension of 

 carmine powder, oil emulsion, and dogfish blood 

 corpuscles were fed to European oysters. He 

 produced convincing evidence that very small 

 food particles are absorbed by the cells of the 

 digestive diverticula, while the diatoms and other 



Mil limeters 



Figure 207. — Longitudinal section of the anus and ad- 

 jacent portion of the rectum. Note the fecal mass 

 inside and the absence of a sphincter. Bouin, hema- 

 toxylin-eosin. 



228 



FISH AND WILDLIFE SERVICE 



