Turner, Mushroom Bodies of the Crayfish. 337 
J. J. Hamaker (’98) has studied exhaustively the nervous 
system of Nereis. The results of his research may be epito- 
mized as follows: 
Throughout the ventral cord is differentiated into ganglia. 
The brain gives origin to the following fourteen pairs of 
nerves: I, nerve to the proboscis; II, nerve to the antenna; 
III, nerve to the dorsal wall of the head; IV, nerve to the 
palp; V, nerve to the ventral side of the proboscis; VI, sen- 
sory nerve to the palp; VII, nerve to the palp; VIII, IX, X, 
roots of the oesophageal commissure; XI, XII, optic nerves; 
XIII, nerve to the ciliated groove; XIV, nerve to the dorsal 
surface of head. In addition to these fourteen pairs of nerves 
there is a median unpaired nerve which passes to the dorsal 
surface of the head. 
In the oesophageal collar there is a ganglion which sends 
nerves to the anterior cirrus, to the proboscis and also a branch 
which, passing forward (cephalad), unites with V to form a 
ganglion. 
The sub-oesophageal ganglion gives rise to three pairs of 
nerves and each other ventral ganglion gives origin to five pairs 
of large and several smaller nerves. . 
The parapodia are innervated almost entirely by the para- 
podial ganglion, from which four nerves radiate towards the 
periphery. 
The following cell nidi are found in the supra-oesophageal 
ganglion: 1, in front, on each side of the brain, between the 
anterior median and the anterior lateral groups of nerves, there 
exists a large ventral anda smaller dorsal group of small cells 
arranged in radiating rows; 2, on the posterior border there is 
a group of spindle-shaped cells with indefinite boundaries; 3, 
along the inner border of 2 there isa group of pear-shaped 
cells with definite cell-membranes; 4, near the meson there is 
a group of pear-shaped cells; 5, at the side of the brain, be- 
neath the anterior eye nerve, there is included in the brain a 
group of cells which seem to have no other connection with 
the brain ; 6, other large cells. 
The central nervous system of Nereis virens occupies a 
