CILIARY MECHANISMS OF LAMELLIBRANCHS 631 
respiratory functions performed by the organ are physiologically 
important, for Schizotherus possesses, well developed, all the 
other organs used by lamellibranchs for these purposes. If the 
vascular fold has other functions, however, that will better ac- 
count for its presence and its great size, they have not been 
observed. 
Freedom of organs in the mantle chamber 
On removing a valve of the shell, it is very noticeable that the 
ciliated organs lie against each other—the mantle against the 
outer demibranch, outer palp, and sometimes the visceral mass; 
the outer demibranch overlies the inner, and the latter rests on 
the visceral mass. The question arises: How is interference 
with ciliary function prevented when ciliated surfaces apparently 
are applied to each other? 
It can be seen in several forms—Pecten, for example—that in a 
natural position, with valves more or less separated, the mantle 
chamber is spacious enough to allow all the organs to extend 
themselves without touching each other. When it is desirable, 
such a position is maintained through muscular action, for all 
gills and palps are capable of complicated and extensive adaptive 
movements. Frequently, when it is of advantage, as when 
an excessive load of material is placed on the gills, these organs 
move so as to touch visceral mass or mantle, and their collections 
are transferred to the surfaces with which contact is made. 
Palps frequently are drawn away from gills so as to avoid re- 
ceiving material from them, and specific instances of these mus- 
cular aids to the ciliary mechanism will be mentioned. 
The mechanism for food collection 
Gills. It has long been known that the floating diatoms which 
constitute almost the entire food supply of lamellibranchs, are 
collected by the gills, passed by ciliary action from them to the 
inner surfaces of the palps, and between these lip-like organs to 
the mouth. The progress of carmine, or other material used 
