192 W. BLAXLAND BENHAM. 
only imperfectly focussed ; hence the outermost ridges appear 
more strongly defined than the rest (see Lankester’s and Vej- 
dovsky’s figures of Psammoryctes), but by careful focussing 
it appears to me that all the ridges are equally developed. 
Now, if one of these cheetz be observed from above during 
life, so that we look down it, we shall of course see the head 
foreshortened, and we have the appearance portrayed in fig. 8. 
This has somewhat the appearance of a cup, one side of the 
cup being formed by the free edge of the teeth, whilst the 
two outer ridges and the thick stalk immediately below the 
head form the curve which may be mistaken for the other 
side of the cup; and I believe this appearance deceived 
Claparéde. These palmate cheetze vary in number on different 
segments, as the following table and fig. 3 show; there is also 
individual variability for each bundle.! The cheete of a bundle, 
when in movement, diverge from one another in a fan-shaped 
manner, the edges of the various chetz almost touch, and 
are so regularly arranged as to form part of a curve. The 
whole bundle is moved backwards and forwards—striking the 
water, that is to say, with the flat faces of the chetz, which 
no doubt serve as oars. It is interesting to note that the 
furcate cheetz are freqnently rotated on their own axes, in 
addition to their to and fro movement; and that not unfre- 
quently the angle between the prongs, which is normally 
directed downwards, is directed upwards. There appears to be 
a much greater freedom of movement in all directions in the 
furcate bundles than in the palmate bundles. 
Although these facts can be to a very great extent observed 
in a living worm, slightly compressed by a cover-glass to pre- 
vent too active a movement, yet it is necessary, in order to 
properly ascertain the character of the chetz, to treat them 
with caustic potash, This I did, and have mounted them in 
glycerine jelly, which, as Professor Lankester has observed, is 
a most useful mounting medium for chete. 
When treated with KHO, however, the embedded ends of 
1 That is, the bundle of the corresponding somite in two or more worms does 
not always have the same number of cheete. 
