30 On Syncheta Mordax. gba see ag 
rotifer in Siebold and Kolliker’s Zeitschrift of Zoology for Novem- 
ber, 1869. The sete are best seen by dark field illumination, and 
when the animal is swimming freely ; but of course only momentary 
glimpses can be caught of them. When S. mordaa# is held in the 
compressorium it never ceases to struggle forwards, jerking every 
now and then its head and mastax inwards by means of its longi- 
tudinal muscles. After each jerk, as the head regains its old posi- 
tion the dorsal setze can be seen to slip back to theirs, and the two 
rocket heads with their corresponding nerve fibres can thus be made 
out. So violently is the head drawn in that the loop which these 
setee form (Fig. 4, b) is thrown forward so that the sete appear to 
belong to the ventral surface ; and it was some time before I could 
satisfy myself as to whether there were setze on that surface or not. 
I expected to find sete at. the root of the tail as they are in S. ére- 
mula; but I do not think that they exist. S. mordaaz puts this 
tactile apparatus to good use, for it will (as I have already men- 
tioned) turn somersets with the greatest rapidity and violence between 
two plates of glass, separated by barely more than its own length, 
without striking against them. The red eye (Figs. 2 and 4, e), if it is 
an eye, can be of little service for such pranks, as it lies behind the 
head and sunk at some depth under the dorsal surface. It is erim- 
son by lamplight, but a bluish-purple by daylight ; it is a truncated 
cone with the broader end downwards, and from this end a tapering 
prolongation passes downwards to the large nerve mass in the head. 
The arrangement of Synchxta’s muscles is very similar to that 
of Hydatina senta ; the two large ones (Figs. 1, b, and 4, c) that with- 
draw the head are attached to the dorsal cuticle and have branches 
(Fig. 1, ¢, c) attached to the ventral cuticle, so that the united pull 
may draw the head down nearly ina line with the creature’s longer 
axis; powerful muscles work the side lobes, and others springing 
from the middle of the animal work the foot and its pincers: trans- 
verse muscles divide the body into segments and enable it to regain 
its shape after it has contracted in direction of its length. 
The mastax (Fig. 6) is enormous; it is similar to that of S. 
tremula, which has been figured by Gosse in the ‘ Philosophical 
Transactions’ of 1856. Fig. 9 shows the harder portions after 
treatment with caustic potash, and compressed out of their normal 
positions ; a, a, are the mallei, each with a solitary sharp tooth jomted 
ate; 6,b, are the ramiandd the fulcrum. The same letters point out 
the same parts in Fig. 8, which is an ideal side view of them in their 
normal position, and in Fig. 7 which is the distended aperture of the 
mastax. 
The mallei are often protruded with a swift snap through the 
mouth, and the rami too are thrust out in front of the frontal out- 
line, and when so extended appear to be connected by some mem- 
brane (Fig. 7,¢): as the mallei regain their position in the mastax, 
