120 Macteay Memortat Vouume. 
occupied by a broad transverse band of fibrous material, through which are traceable 
numerous nerve-tubes ; the nerve-cells are now collected into two groups, which are 
wide apart and external to the eyes. On a somewhat deeper plane the lateral groups 
the former 

of nerve-cells begin to be divisible into an anterior and a posterior set 
connected with the anterior, the latter with the posterior, series of peripheral nerves. 
At a still lower level the ganglion-cells become fewer ; and the fibrous band exhibits 
very large spaces and channels which are quite symmetrically disposed on either side 
of the middle line; here the central mass assumes an investment, apparently of the 
nature of parenchyma muscle, on its anterior and posterior surfaces; the spaces 
increase in size towards the ventral surface of the brain. 
On carefully going over such series of sections and comparing them with 
longitudinal, vertical (Pl. x1. fig. 8), and transverse series, it becomes evident that the 
nerve-tubes which enter either side of the central fibrous mass in great measure 
coalesce to form the large symmetrically disposed spaces and channels which are filled 
with the same extremely delicate material that occupies the interior of the nerve 
tubes themselves. There are thus two entirely different elements to be distinguished 
in the “ Punkt-substanz” of the brain-ganglion: (1) a tolerably dense reticulum of 
fibrous material, through which run many nerve-tubes ; and (2) a series of channels 
of comparatively large size containing delicate, readily altered material similar to 
that which fills the nerve-tubes. The relative position and arrangement of these 
two elements are shown in fig. 8 of Pl. x1. 
In the arrangement of the peripheral nerves of Zesenocephala a remarkable 
feature is the large development of the nerve-cords which run forwards from the 
ganglion—this being co-ordinated with the presence of the tentacles, into the base of 
each of which a large nerve enters. * 
Posteriorly there are given off three pairs of longitudinal cords—a dorsal, a 
dorsi-lateral and a ventral. The first of these, which is smaller than the others, is 
superficial in position, lying immediately underneath the longitudinal layer of muscle. 
The two cords leave the cerebral ganglion at its posterior and lateral angles, and run 
backwards along the dorsal aspect parallel with one another, connected here and 
there by transverse commissures. Externally branches are given off at tolerably 
regular intervals; these ramify and the ramifications anastomose, giving rise to a 
network of nerve-branches extending outwards to the lateral border. In 7° guad- 
ricornis, if not in the others, there are occasional ganglion-cells in the course of these 
branches. 
* Weber (l.c. p. 23) remarks on the large size of these cords as represented in my fig. 6 of pl. xx.; but, though the 
whole of that figure is diagrammatic and intended only to show the general relations of parts in the genus, there is little 
exaggeration in this respect. 
