466 
BULLETIN OF THE BUREAU OF FISHERIES. 
TIME REQUIRED FOR PASSAGE OF FOOD THROUGH THE ALIMENTARY CANAL. 
From experiments previously described (p. 454), material was found to pass 
through the alimentary canal in somewhat less than 1 hour. In another case 
(p. 455) carmine grains passed through in an hour and 10 minutes. Approximately 
the same results were obtained in several experiments with juvenile mussels from 
2 to 4 mm. in length. 
In larger specimens, even those as long as 25 mm. in certain species, the valves 
are so thin that one can ascertain by holding the mussel up to the light whether the 
rectum is filled or empty. If filled, it will appear as a dark brown or black thread 
extending from the point anterior to the heart where it emerges from the visceral 
mass to the anus. If empty, it will appear pale or colorless. Specimens may be 
kept in filtered water until the rectum is seen to be empty and then placed in 
various cultures containing food or other materials, and almost the precise moment 
ascertained when the first waste material reaches the anus. 
A specimen of Anodonta grandis about 15 mm. long, with rectum empty, at 
9 a. m. was placed in filtered water in a container the bottom of which was cov- 
ered with a layer of mud and sand. The water contained in suspension particles 
from the sand and mud, including probably some organic forms. At 2 p. m., or in 
five hours, the rectum was filled nearly to the anus with black material, which had 
been ingested from the suspension. The mussel was then placed in clear filtered 
water, and at 4.45, or in two and three-fourths hours, the rectum was empty. 
A specimen of A. grandis 25 mm, long, the rectum empty, at 8.45 a. m. was 
placed in a culture the bottom of which was composed of river mud. The water 
was thick with suspended material, part of which was fine particles of mud. The 
water remained quite turbid all through the experiment. The mussel began crawl- 
ing at about 9 a. m. At 10.15 nothing could be seen in the rectum, but, through 
the valves, masses of dark material could be discerned upon the palps. At 11.40 
the rectum was filled within about 1 mm. of the anus. 
Three mussels from 15 to 20 mm. long were kept in suspensions of borax 
carmine for periods varying from one and one-half to three hours, in which periods 
the rectum became completely filled. The entire length of the intestine could be 
traced without dissection owing to its bright red color. Taken as a whole, the 
experiments show that in juvenile mussels a particular particle of material passes 
through the alimentary canal in from one to five hours, varying roughly with the 
size of the mussel. 
GENERAL CONCLUSIONS. 
1. In the small juvenile mussel, from 0.2 mm. to perhaps 2 mm. in length, 
before the siphons have developed, material drawn in by the cilia on the gills passes 
between the valves at points from the midventral side to the anterior end. 
2. Before the outer gill has developed, the material falls upon the inner gill, 
passes down to the ventral groove, and forward to the palps. After the outer gill 
has developed the material that falls on the outer side of that gill moves up to the 
dorsal edge and forward to the palps. That striking the inner side moves up to the 
dorsal edge, is transferred to the inner gill, and moves down, together with the 
