174 Proceedings of Poijal Soeiety of Edinburgh, [march 5, 
is quite a parallel case in the ciliated epithelium of our own bodies, 
say of the lining membrane of the nose or of the windpipe, for, not 
only does this ciliary motion continue when the epithelium is 
scraped olf and mounted in water, and not only may the motion 
persist for days, hut detached cells or even groups of cells of the 
epithelium may swim about freely on their own account. There is 
this important difference, however, in the sea-mussel, that it is not 
merely subordinate parts which are capable of independent loco- 
motion, hut large and conspicuous organs of the body. 
And lastly, it will he interesting to determine the function of the 
parts when attached to the body, in so far as that function depends 
on movement, judging from their behaviour when free, and to see if 
such movements can throw any light upon their actions when in 
organic connection with other parts. 
Origin of the Present Inquiry . — While examining the sea-mussel 
in the ordinary course for medical students at the Biological Labora- 
tory, Ormond College, University of Melbourne, the gills came in 
for their share of study, not only to determine their minute structure, 
but to observe the beautiful play of cilia. Eecognising the import- 
ance of seeing ciliary motion as far as possible under natural condi- 
tions, each student was directed to detach a portion of the gill, and 
examine it uncovered under a low power of the microscope. It was 
soon discovered that the rapid rhythmic motion of the countless 
cilia continually drove the portion under observation from the field 
of view, and at first I was inclined to attribute such an unlooked- 
for motion to the flotation of the thin membranous portion of the 
gill in the liquid necessary for mounting. It soon became evident, 
however, on introducing the eye-piece micrometer, and noting the 
rate of motion over a measured distance, that the movement was 
pretty regular and in the same constant direction. The cilia seemed 
to propel the mass like so many oars all acting together, and with 
measured stroke. The naked eye was next called into requisition 
to observe the movement, in this instance truly making that which 
should have been first, last. Suffice it to say, that the clue was 
promptly followed up, and unexpected movements and modes of 
motion revealed themselves in other parts as well, even in the entire 
animal. 
The course of the investigation, in fact, is a striking instance of 
