OF MYRIAPOD A AND MACROUROUS ARACHNIDA. 
257 
readily miscible in water, and more easily destroyed than the fibre of the cord itself; 
and that they usually break off (fig. 8.) on injury at their junction with the longitu- 
dinal portion of the cords, thus further leading to the inference, that in these parts 
the nervous substance is less consolidated, and that the growth of the structure is 
effected at these places. This view of the gangliated portions of the cord in Articu- 
lata may perhaps be extended to those of the cord in Vertebrata, seeing that in both 
there is an accumulation of gray nucleated cells in each enlargement. May not the 
office of these cells be to supply means of growth for the cord itself, and also for the 
large nerves distributed from the cord in those regions ? 
The Geophilidcc (fig. 11.) present a condition of the nervous system similar to that of 
the Polydesmidce, in the size and distinct form of the ganglia, but they approach also 
to that of the lulidce in the uniformity of distance of the ganglia from each other, 
and in their great multiplicity. Their number varies much in different species and 
subgenera. In some instances, in Mecistocephalus , Newport ( Geophili maxillares , 
Gervais), there are not more than forty-six, but in Geophilus subterraneus, Leach, 
there are eighty-six, besides those of the brain ; and in a new genus, Gonibregmatus, 
Newport*, there are even so many as one hundred and sixty. In the higher forms 
of Chilopoda, as in Scolopendra, there are only twenty-three; and in Lithobius and 
Scutigera fifteen, besides the brain and medulla. 
In Geophilus subterraneus (fig. 11, 12.) the brain ( b ) exhibits a condition similar 
to that of Polydesmus, in the almost entire absence of optic nerves. But it differs 
in the fact that the optic ganglia (c) are slightly developed at its sides, and that these 
give off a very minute filament to the single ocellus, which exists on the under side 
of the head, behind the antenna. Treviranus'|~ has described the brain in Geophilus 
longicornis , Leach, as entirely without organs of vision ; but from the existence of 
an ocellus in that species also, on each side behind the antenna, he has probably over- 
looked its minute nerve. The brain itself is large, as compared with the size of the 
head, and the ganglia of the antennae ( a ) have almost completely coalesced with it. 
The nerves of the antennae are also exceedingly large, and, as in Polydesmus, seem to 
compensate for the imperfection of vision, by appreciating the condition and proximity 
of surrounding objects by the sense of touch. Each nerve appears to have a small 
g'angliforrn enlargement of its structure in every joint, from which branches pass off 
directly to the muscles. This is a condition of the antennal nerve not before met with 
in the Myriapoda. The crura which pass down from the brain are long and slender, 
and the medulla (d) with which they are joined is considerably larger than any of the 
other ganglia, the first fifteen or twenty of which are much closer together than in the 
middle portion of the animal ; thus further showing the constant tendency of those 
ganglia, and parts of the cord that have acquired their full dimensions, again to ap- 
proximate and unite. The form of these anterior ganglia is slightly different from 
that of the posterior. They are rounded, and give off one pair of nerves at their front ; 
* Proceedings of Zoological Society, Dec. 1842. f Loc. cit. tab. vii. fig. 5. 
