20 UNITED STATES NATIONAL MUSEUM BULLETIN 296 



the esophagus and mouth, either by violent contractions of the 

 entire body and mantle to put pressure on the stomach; or by reverse 

 peristalsis in the esophageal region, "milking," as it were, the contents 

 back out at intervals. 



To solve the first question as to whether ingestion of indigestible 

 items occurs I tried feeding the barnacles various substances by 

 saturating anything they might ingest with these substances. Car- 

 mine, bone charcoal, "Aquadag," and "Higgins Eternal Ink" carbon 

 particles were tried. It was found that the latter was the most effective 

 when allowed to stand long enough to allow the ammonia in this 

 product to escape. 



The barnacle would ingest sizable quantities of the ink particles 

 when immersed in a 10- to 30-percent solution of ink in sea water for 

 periods of several hours to four days. Of course at this concentration 

 they had little choice of ingesting anything without taking in carbon 

 particles, but at least under these conditions indigestible particles 

 were ingested, rejecting the first hypothesis. 



Investigation of serial sections of normal females of different sizes 

 not subjected to any artificial particles did not reveal any gradation 

 of accumulation of debris in the gut, as would be expected if the females 

 retained indigestible material until death. The second hypothesis, 

 therefore, is rejected. 



Similarly, voiding of discreet particles such as carbon particles by 

 phagocytosis, or other means through the mantle wall, should be 

 evident in the serial sections of those ingesting ink particles, but no 

 evidence of this was seen in a total of 56 animals. Hence, the third 

 hypothesis seems to be rejected. 



The most probable answer occurring to me is that the contents are 

 regurgitated back through the esophagus and mouth. As has been 

 indicated, this could be brought about by violent contractions of the 

 entire mantle, or by reverse peristalsis in the esophagus. The latter 

 process was investigated without success by trying to observe the ac- 

 tion of the esophagus in living specimens with a portion of the shell 

 removed. Vital dyes were introduced to aid in this study with no 

 success. Animals were placed back into fresh sea water after a period 

 of time in ink solution, and then killed and sectioned at intervals 

 (see table 1) to see if the emptying of the ink was a gradual or spasmodic 

 occurrence. The results inconclusively pointed toward a gradual 

 elimination of the carbon, but inasmuch as discharged carbon could 

 still be in the mantle cavity and could be reingested, and in view of 

 the fact that more carbon was invariably found in the mantle cavity 

 than in the stomach, no decisive conclusion can be drawn. 



Methods: Thirty-two adult (over 0.5 mm aperture) Uving Trypetesa 

 lateralis females were placed in 1 inch of sea water to which 10-percent 



