ON PENNELLA BALZINOPTERZ. A417 
chitinous wall of the head inclosed three objects 
a pair placed laterally, which 
were readily coloured by carmine (fig. 8, g), and one placed mesially next the ventral 
surface, which did not take the carmine dye (fig. 8, V). 
The red stained bodies were recognised in sections through the head as high 
as the sides of the oral chink, and were obviously nerve ganglia. At their upper 
end they were separated from each other by the mesial oral chink, the tubercles 
connected with its walls and the areolated tissue associated with the tubercles. 
Hach was placed close to the common tendon of attachment of the bundle of striped 
muscular fibres already described on each side of the head. In the upper part of 
a ganglion not more than six to twelve characteristic cells could be seen in the 
plane of section, but opposite the lower end of the oral chink the ganglion increased 
in size and the cells were much more numerous. Immediately below the oral cleft 
the ganglia were relatively large, and were situated partly to the side of the cesophagus 
and partly ventrally to it, but they were not continuous with each other on the 
ventral surface, as they were separated by the mid-ventral object which did not 
take the carmine stain. The ganglia were traced in successive sections as far as 
opposite the origins of the arms, but they were not visible in the sections immediately 
below the arms, where their place was occupied by areolated tissue. It was noticed 
that where each ganglion had a wide transverse diameter, it was not unusual for the 
cells in its centre to show signs of disintegration; and sometimes this was so ex- 
tensive that a cavity had formed, the wall of which was irregular and showed no sign 
of a lining membrane (fig. 8, 9, 9). 
When examined under a high magnifying power the structure of the ganglion cells 
was readily recognised. The nuclei were large and oval in shape, and as they stained 
a deep red with carmine, they were very distinct, and an intranuclear network of 
fibrillee was present in them. The cell-plasm was granulated. The best-marked cells 
were considerably larger than the motor cells in the lumbar enlargement of the human 
spinal cord, though others were very much smaller. The bodies of the cells were 
polygonal, and from the angles delicate processes of the cell-plasm projected. As a 
rule, the cells were closely aggregated, and it was difficult to trace these processes for 
any distance, but they were sufliciently distinct to leave no doubt of the multipolar 
character of the cells. In places minute intercellular intervals were visible, and the 
outlines of the cells were defined by a distinct wall. Although the relative proportion 
of the nucleus to the cell-plasm varied in the cells, it was evident that in the largest 
cells the cell-plasm exceeded three or even four times in quantity the size of 
the nucleus (fig. 15). 
From the character of the cells there can, I think, be no doubt that the red stained 
bodies were a pair of nerve ganglia. Their position in the head, their relation to its 
ventral surface and to the cesophagus, localise them as cesophageal ganglia, situated 
laterally and ventrally to the gullet, though not united to each other on the ventral 
aspect of the cesophagus. When portions of these ganglia were removed, teased with 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART II. (NO. 18). 62 
