21G Transactions of the Royal Microscopical Society. 
conventional forms we can pass from one to the other of the groups 
referred to and distinguished in this particular by Mr. Cubitt * and 
Mr. Davis, t 
Eeturning now to M. ringens and its building apparatus, I 
agree with Mr. Cubitt that the united stream brought down 
by the two Y-shaped ditches is subjected to a process of inves- 
tigation at the point where the two tides meet, and that the edge 
of each Y-shaped collecting ditch or secondary lip concludes with a 
blunt organ like a knotty protuberance set symmetrically one 
against the other ; two janitors, in fact, to watch the stream, and 
which only allow those particles to pass that are fit either for 
“eatable” or “mural” purposes, and which stop all the rest, sending 
them off at a tangent as “ waste ” over the main chin (see diagram, 
PI. CXCVII., B) where these organs are represented by two triangles 
with the apices downwards ; but below these blunt protuberances I 
place another organ, for the stream which passes the blunt protu- 
berances bounces down with great force on to a “ cushion ” of 
hemispherical shape placed at an angle on that side of the sinus 
or “ hopper ” which is opposite to the main chin, and as I cannot 
represent the natural appearance of this cushion by any effort of 
the pencil, I have shown its position in the diagram by a cubical 
figure placed at a suitable angle. From this cushion I make out 
certainly three, and sometimes four deflected streams : one glances 
off and shoots down as “ food” to the mastax ; a second sometimes 
goes off at a perpendicular over the main chin, that is “ waste ” ; 
and the third and fourth go off at slight angles to the last, one on 
one side of it, and the other on the other, and these two last are 
the “ mural ” streams passing over the side chins and going to the 
pellet organ. Now, the action of this cushion is most striking, for 
if I am right, it is highly sensitive, and by altering its facial confi- 
guration with startling rapidity, it distinguishes between all these 
four streams respectively, and drives suitable particles in appro- 
priate directions. 
If now we follow the two currents that go from this cushion to 
the side chins, we must try and carry with us in imagination the 
size of the animal, and the space at our disposal, and we must 
remember that close over head, so to speak, is a roaring rush of 
“ waste ” particles tearing away from the blunt protuberances and 
threatening to sweep away the delicate fragments required for 
the pellet organ, and then consider how the safe passage of those 
fragments to that organ is to be ensured. And here I introduce a 
further arrangement ; along each side of the sinus or “ hopper,” as 
I have called it, and running at an angle from each side of the 
cushion to each side chin, is a ditch (or chase as Sir. Cubitt calls it) 
of cilia, along which the pellet fragments travel, this anyone can 
* ‘M. M, J.,’ vol. viii. p. 5. f Ibid., vol. xvi. p. 1. 
