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BULLETIN OF THE BUREAU OF FISHERIES. 
Possibly some deductions might be drawn from the experiments of Churchill 
(1916) on the ability of fresh-water mussels to absorb nutriment from solution. 
Working on adults he came to a number of conclusions that are of interest in con- 
nection with the nutritional phases of the larva, since the correlations of tissues 
and functions must be very similar. With fats as emulsions, dissolved proteins, 
and starch in solution he came to the conclusion that the adult mussels are able to 
take up food directly from solution; that the outer epithelial cells of the body 
possess this ability to some extent, and in this connection he makes the following 
observation : 
As these animals are provided with a well-developed digestive apparatus, we may suppose that 
the absorbing power of these epithelial cells is a property that has been retained from a more primitive 
state in which the cell was less highly specialized, and that this property is not a special adaptation 
correlated with the lack of a functional digestive system. 
Nutriment from solution could also be taken up by the alimentary canal, 
which, of course, is highly specialized for this purpose. Although uncertain as to 
the nature of the absorption of the foods by the epithelial cells he concluded that 
this may have been effected by phagocytic or amoeboid action of the cells or by 
solution in the plasma membrane and reprecipitation within the cells. Granules 
of albumen were carried entire to the interior of the cells, supposedly byphagamoe- 
boid or phagocytic action. Possibly in referring to the “ primitive” origin of the 
nutritional capacity of the epithelial cells, Churchill may have had reference to the 
encysted larvae, and even though this is not the case, it is interesting to note how 
applicable his words are in connection with the nutrition of the developing larva, 
where all the epithelium is bathed in body fluids of the host and where an absorbing 
power by the cells is evident. This would seem to bear out the belief that during 
the latter stage of development of the larva the definitive mantle is a nutritional 
organ and also seems to give some reason for considering that the developed ali- 
mentary canal also may function in this manner to a limited extent. 
COMPLETION OF DEFINITIVE MANTLE. 
During the latter third of the parasitic period the mushroom body is pushed 
more to the center of the valve, due, apparently, to the development of the definitive 
mantle, so that the base of this body becomes smaller, with the overflowing appear- 
ance more pronounced. However, a gradual reduction in size of the mushroom 
body takes place, since its substance is absorbed and utilized as food, and finally 
toward the end of the parasitic period it disappears altogether, with the definitive 
mantle becoming complete at the same time. This marks the end of the regeneration 
process of tissue formation of the developing larva, in which the larval adductor 
and the larval mantle were so largely concerned. From now on development 
proceeds in a normal manner. Both anterior and posterior adductor muscles 
appear, the alimentary canal becomes a completely connected organ with large 
fiver sacks, the lateral pairs of gill buds become conspicuous, with complete ciliation, 
the foot projects widely into the mantle cavity, a lymphatic system is developed, 
leucocytes make their appearance, with the heart and kidneys becoming noticeable, 
and the ganglia take on an extensive development, so that by the time the young 
mussel is liberated it has become a miniature of the adult, with practically all the 
adult organs in evidence. 
