1888 .] 
Mr D. M'Alpine on Bivalve Molluscs. 
201 
In the one case, the cilia send matters to one side, in the other they 
send food down the gullet ; and it may be that the relaxation or 
stretching of the labial palps has to do with the opening or closing 
of the mouth. It may be objected to this view, that there is no 
selecting of suitable food before the mouth is reached, but after 
passing through the efficient strainer of the tentacular margin of the 
mantle-lobe, only relatively small particles will be carried forward, 
and that is the main selection exercised, the lips doing the rest 
before allowing it to enter. The indigo-particles were swallowed, 
although they were not food, but they were afterwards ejected along 
with the faecal matter. Indeed, the mussel is not particularly 
fastidious, nor are its wants difficult to supply, as it even makes 
use of its own generative products, as does the oyster. 
The main purpose of the labial palps will be to clear away intro- 
duced matter that might otherwise clog up the body — one palp to 
intercept the strained matter of each gill ; and in a sedentary animal, 
with streams of tidal sea-water periodically flowing in, this is quite 
as necessary an operation as the aeration of the tissues or the actual 
supply of food ; in fact, it renders these operations easy of accom- 
plishment and certain in effect. 
If asked. How does food get into the mouth of Mytilus I would 
reply that the counter-currents of the muscular margin of the 
mantle-lobe carry forward food-particles in their stream, and the 
ingoing in conjunction with the outgoing currents create such an 
eddy at the anterior end as to bring within reach of the mouth 
abundance of food. Once there, the lips can reject whatever is 
unsuitable, if not presented in too large quantity, or pass along 
whatever is suitable. Whether this view be accepted or not, I 
trast that its being brought forward may lead to more attention 
being paid to the food and mode of feeding of Lamellibranchs. 
The ciliary action is sufficient to move the mantle-lobe weighing 
about 5 grains in a horizontal direction at the rate of one mile in 
88 days, or in a vertical direction one-fifth of a mile in the same 
time. Comparing these figures with those obtained by Wyman and 
Bowditch {Bost. Med. and Stirg. Jour.^ August 10, 1876), it may 
be calculated that the force of the ciliary motion in the sea-mussel 
is to that of the frog’s palate, &c., is as 18 to 5, or nearly four times 
as great. 
