Mastax M. ringens, &c. Lord S. G, Osborne and F. A. Bedivell. 181 
dotted lines where it passes beneath the central blade. In nature 
this blade is quite transparent, and the alulse can nearly always be 
seen by focussing through. Facing the lowest angle of each alula 
at the point c, will be seen the extremity of a circular arm, e, and 
this extremity in life is rigidly joined to the alulse at the point c, 
where I have severed them. These two circular arms spring from 
a hinge, H, where I have, for distinctness, again separated parts 
which in nature are joined; from that hinge springs upwards a 
!i handle which is articulated to the two circular arms, and starts 
I backwards and upwards, just as the armed prong of a spur starts 
j from the horseshoe-like arms which pin the spur to the heel. The 
handles of the ramus are seen above, meeting together at a second 
hinge, K, where they coalesce and bend down to meet the point of 
the spur as it rises upwards. The hinges H and K in the living 
animal are imbedded in the large globular mass of muscle which 
occupies this part of the mastax, and are consequently difficult to 
decipher. 
When the jaws are in action the two handles of the ramus 
spring together sharply at the hinge K, and this action brings the 
frontal blade of each ramus into contact, and so brings the teeth 
I together, but it brings them together fomt to foint. But foint to 
point is useless to the animal, and it is necessary that the teeth 
should be tilted up from behind, and their points depressed, so that 
I the upper surfaces of the teeth may grind on each other, like a 
I knuckle on a knuckle, and so that the prominent projecting surface 
edges of the teeth in one jaw may fit into the depressions which lie 
between the teeth in the other, like a series of WW^ meeting each 
other, angle to angle. It is here that the action of the alulae 
begins, and a little consideration of Fig. 6 shows that if the angle 
c of each alula is raised upwards ever so little, while the main 
handles of the rami are kept closed and pressing against each 
other, then the free edge of the central blade of the ramus must 
j go up, while the points of the teeth must come down. 
Now, in action the point of each alula is in fact thus raised, 
and it is elevated by the circular arm ee of the spur to which 
in life it is attached at the point c, and from which I have severed 
it ; and these arms, by moving upwards on the hinge H, tend to 
rise out of a horizontal plane into a perpendicular plane and to take 
up the position seen in Fig. 7, which is an extreme view of this 
elevated attitude. As already mentioned, I had anticipated, from 
what Mr. Gosse said of muscles attached to alulse in other rotifers, 
that we should find in Conochilus and M. ringens a dragging force 
acting by muscles at the angles of the alulw (see Fig. 3, Plate X.), 
instead of which it is simply a pushing force ! I did make a mistake 
in my deduction, but it was one of a most satisfactory character. 
The action of the alulse will be further appreciated by an 
