NOTES ON SOME AQUATIC OLIGOCHATA. 195 
fications of the furcate or crotchet-shaped chet, with the 
multidentate forms as an intermediate condition. 
I am inclined to regard them in a different light, for— 
(a) If a palmate bristle be viewed from its edge, I have 
shown that the tips of the teeth are all curved, and this curve 
resembles the curve of a furcate cheeta if the lower tooth were 
removed. 
(6) The divergence of the two outer teeth or ridges of the 
comb is different from that of the prongs of the fork, in which 
both prongs are directed towards the same side of the stalk, 
and the tip of each is frequently curved downwards in the 
same direction. In the palmate bristles it will be seen that 
neither of these things occurs (see also Pl. VII, figs. 33, a, 
b, 36, c, d). 
(c) The plane of the head, i.e. the two prongs of the furcate 
cheta, is in a state of rest parallel with the long axis of the 
body, whereas that of the palmate bristle is at right angles to 
the axis of the body. 
(d) The so-called “intermediate” forms, or “multidentate ” 
forks, do not represent a stage in the formation of the ctenate 
bristles. The two prongs are similar to those of the simple 
furcate forms in relative size, curvature, divergence, &c. 
(e) I would rather regard the ctenate cheta as having been 
derived from a simple “‘ sigmoid”’ cheta (such as is common 
amongst earthworms, some Lumbriculidez, some Enchy- 
treidz, and in Phreoryctes) by a flattening and expansion 
of the dorsal extremity, so as to form the ‘‘ membrane,” which 
then becomes thickened or ribbed to give rise to the palm-leaf- 
shaped arrangement; whilst the furcate cht, which are so 
common amongst the Oligochzta generally, may have been 
derived similarly from the ‘“‘sigmoid’’ form by the appearance 
of a notch at the extremity, which became deepened to form 
the angle between the two prongs, these in their turn becoming 
more and more developed, the plane of two prongs being at 
right angles—with respect to the axis of the original cheta— 
to the plane of the “membrane” of the palmate forms. 
The “ multidentate ” chzetz will then be a further develop- 
