BULLETIN OF THE UNITED STATES FISH COMMISSION. 417 



represented by a single organ in the oyster. In fact experiment has 

 shown that the secretion of the liver of mollusks combines characters 

 of at least two if not three of the glandular appendages of the intestine 

 of vertebrated animals. There are absolutely no triturating organs in 

 the oyster for the comminution of the food ; it is simply macerated in 

 the glandular secretion of the liver and swept along through the intes- 

 tine by the combined vibratory action of iunnmerablc fine filaments 

 \nth. which the walls of the stomach, hepatic ducts, and intestine are 

 clothed. In this way the nutritive matters of the food are acted on in 

 two ways: first, a peculiar organic ferment derived from the liver re- 

 duces it to a condition in which it may be absorbed ; secondly, in order 

 that the latter process may be favored it is propelled through an intes- 

 tinal canal, which is peculiarly constructed so as to present as large an 

 amount of absorbent surface as possible. This is accomplished- by a 

 double induplication or fold which extends for the whole length of the 

 intestine, the cavity of which, in consequence, appears almost crescent- 

 shaped when cut across. On the concave side, the intestinal wall on 

 its inner face is thrown into numerous very narrow, longitudinal, and 

 interrupted folds, which further increase the absorbing surface. Such 

 minor folds are also noticed in the stomach, and some of these may even 

 have a special glandular function. There are no muscles in the walls 

 of the intestine as in vertebrates, but the sole motive force which propels 

 the indigestible as well as digestible portions of the food through the 

 alimentary canal is exerted by the innumerable vibratory cilia with 

 which its inner face is clothed. 



This apparatus is admirably suited to render the microscopic life found 

 in the vicinity of the animal available as a food supply. The vortices 

 created by the innumerable vibratory filaments which cover the mantle, 

 gills, and palps of the oyster, hurl the microscopic edible hosts down 

 the capacious throat of the animal, to undergo conversion into its sub- 

 stance, as described above. The mode in which the tissues may become 

 tinged by the consumption of green spores, diatoms or desmids, it is 

 easy to infer from the foregoing description of the digestive apparatus 

 of the animal. The colorless blood cells, moving in a thin liquor san- 

 guinis, would, judging from their amoebiform Character, readily absorb 

 any tinge acquired by the latter from the intestinal juices. The color 

 in them is, however, homogeneously distributed through the substance 

 of the green cells, and is not due to the presence of any organisms or 

 particles within them. No bacteria or putrefactive organisms were ever 

 observed by me in oysters except in such as were spoiled or putrid. 



1 have discussed in another place, in a desultory way, the microscopic 

 marine fauna of the Chesapeake Bay, where I have been engaged upon 

 the study of the oyster under the auspices of the United States and 

 Maryland Fish Commissions, but what I have done has been simply pre- 

 liminary, and necessarily incomplete. Before we are ready to deal with 

 the matter on which the oyster feeds, we desire a more perfect acquaint- 

 BuU. U. S. F. C, 81 27 Aii§^. 8, 1889. 



