ANATOMY OF THE EARTHWORM. lil 
plying the muscles of the anterior segments, are lost in the 
integument of the lower lip. The rest take nearly the same 
course. But what is extremely interesting is that the roots 
of the nerves of this the posterior set are continuous across 
the crus with those of the anterior set belonging tothe supra- 
intestinal chain. 
The subventral chain of ganglia forms with its nerves the 
sub-intestinal portion of the nervous system. It is a double 
cord, gangliated at short intervals by the addition of vesi- 
cular substance and extending from the third ring through- 
out the body. Anteriorly the cords are divergent and form 
the two pharyngeal crura, posteriorly they become closely 
cemented along the middle lme. The ganglionic enlarge- 
ments vary in shape, size, and approximation, at different 
parts. Each gives off from its sides two pairs of nerves, 
which, after sending some filaments to the diaphragmatic 
muscles and bands, supply the longitudinal circular and 
oblique muscles of the rings midway between the ganglia ; 
the intervening cords give off a single pair, which are dis- 
tributed to the deep muscles on each side (see fig. 6). 
The cephalic nerves, which take their origin in one of the 
trunks on either side, into which the bilobed supra-pharyn- 
geal ganglion divides, are distributed to the lower surface of 
the first segment, forming a very delicate organ of touch; 
another portion of the nerves forms a curious plexus in the 
pigmentary layer, and is connected with the large clear cells 
there met with. Mr. Clarke suggests the possibility of these 
forming a mechanism adapted to the perception of diffused 
light, though not of distinct vision. That the first segment 
of the worm, with its nervous plexuses, does form a very im- 
portant organ of perception, there can be no doubt. 
Structure of the Nerves and Ganglia.—In fig. 8 nerve- 
cells and a portion of a nerve-fibre from the sub-ventral 
chain are drawn. In fig. 7 a portion of the cord, less highly 
magnified, is represented. The structure of the various parts 
of the nervous system of the earthworm, as studied by Mr. 
Clarke, has yielded most interesting and important results. 
Each lobe of the cephalic or supra-pharyngeal ganglion is a 
pyriform sac, which is very thick and convex posteriorly, 
where it is partially separated from its fellow by a deep 
notch. This convex portion is opaque white, and filled with a 
mass of semifluid granular substance, and oval, round, and 
pyriform cells of various sizes, but often very large. The an- 
terior half, by which the lobes are joined, is merely lined by a 
lamina of cells, and only at its upper part, its under side 
having a cell here and there. ‘The interior of this portion is 
